The cell reproduced and the organism grew.
In every cell of your body except your red blood cells exists a copy of your DNA.
In 1902, an American named Walter Sutton noticed that chromosomes duplicated themselves before cells divided so that each new cell had a full copy of the chromosomes.
We were startled by the ring of my cell phone.
I tried to call you on your cell phone, but I didn't get an answer.
My cell phone alerted me to a message.
Each cell measures 35 cub.
He took her to the holding cell.
Rhyn made a racket in his cell.
I have more freedom than you when I'm not in this cell.
The animal cell can absorb its carbohydrate and proteid food only in the form of carbohydrate and proteid; it is dependent, in fact, on the pre-existence of these organic substances, themselves the products of living matter, and in this respect the animal is essentially a parasite on existing animal and plant life.
When Ne'Rin signaled all was ready, he strode from the deck into the corridor and straight to her cell.
The cell where she sat measured six by six with a grey bench.
The 'holding cell' was a lavishly appointed 700 square foot room.
Connor's description of being in the holding cell 'losing his mind and living a nightmare' accurately described his feelings.
Elisabeth stared straight ahead, then picked up her cell phone and walked out of the kitchen.
They walked in silence to the holding cell.
He slunk down to the holding cell to face the music.
Okay, let me give you my cell number.
The three sat in the kitchenette of the holding cell since Sarah refused to leave Connor, even for a minute.
He found Sarah and Connor on the sofa in the holding cell.
Maybe you could just give me her cell number.
Toby huddled against the black stone wall of his cell in Hell.
Ully called from the cell across the narrow hallway.
Toby looked up as the familiar demon named Jared passed his cell, trailed by two demons carrying a body with another familiar face.
His long time friend, the assassin, was bloodied and unconscious. The demons tossed Gabriel's body into a dark cell two down from Ully's before they left.
Gabriel's furious curse made Toby jump. Toby looked his direction the best he could through the bars of his cell and saw the walls around the dark cell shake.
Toby asked, pressing his face against the cell door.
Do you have your cell phone?
Keep your cell phone handy.
The somatic cells represent communities or republics, as it were, which we name organs and tissues, but each cell possesses a certain autonomy and independence of action, and exhibits phenomena which are indicative of vitality.
Still, it must be borne in mind that this alleged autonomy of action is said to be founded upon an erroneous supposition, on the supposition that each cell is structurally, and it may be said functionally, separated from those in its neighbourhood.
It is well known that in the vegetable kingdom the protoplasm of one cell frequently overflows into that of cells adjacent - that there is, as it were, a continuous network of protoplasm (idioplasm of Nageli) prevailing throughout vegetable tissues, rather than an aggregation of isolated units.
Until, however, further evidence is forthcoming in support of this syncytial theory of structure, it would be unwise to regard it as established sufficiently to constitute a serviceable working hypothesis; hence, for the time being, we must accept the assertion that the cell represents the ultimate tissue-unit.
Our present day definition of a cell is a minute portion of living organized substance or protoplasm.
The cell body, or cytoplasm, is apparently composed of a fine reticulum or network, containing within the meshes a soft viscid, transparent substance, the cell-sap, or hyaloplasm, which is probably a nutrient material to the living cell.
Usually the cytoplasm shows a marked affinity for the acid stains, but the different bodies found in the cell may show great variation in their staining reactions.
Cell in a state of degeneration and chromatolysis; the large rounded body in the cell is a cancer parasite.
Pigmented cell with resting nucleus.
Then we have the property of adaptation, in which the negative reaction may be changed into a positive; a given toxin may at first repel the cell, but by a gradual process the cell becomes accustomed to such a toxin and will move towards it.
Where the material is too large to be taken up by an individual cell, the dissolution is brought about by the cells surrounding the material, to which they closely apply themselves, and by the secreting of the ferment, a gradual process of erosion is brought about with ultimate absorption.
We have already compared the body to a social community, each constituent element of which - the cell - lives its own life but subordinates its individuality to the good of the whole organism.
The epithelial cells are then able to pass from their normal position, in consequence of which they proliferate and at the same time revert to a more primitive type of cell.
Hansemann's "anaplasia " hypothesis seeks to find an explanation of the formation of new growths in the absence of the histological differentiation of the cell associated with a corresponding increase in its proliferative power and a suspension, or loss, of its functional activity.
This splitting up of the fats previously combined with albumin in the cell by the action of natural ferments - lipases - and the setting free of the fats under the influence of toxins represent the normal and the pathological process in the production of so-called fatty degeneration.
Midnight was long past when Savonarola was led back to his cell.
The sounds of Rhyn slamming his body into his cell and snarling awoke her sometime later.
He retreated to his cell and sat against the wall again, troubled by a familiar feeling of helplessness.
She eyed the door at the end of the hall, then her cell, and turned 360.
She'd lived through too much the past few days to be eaten by some boogeyman in a dark cell!
She dressed quickly to avoid comments on either her collar or her scars and flung herself into her bunk, reminded of her cell with Lankha.
She didn.t remember him being so tall in Hell, but she.d been afraid to look too hard at him when she passed his cell.
She.d last seen him in Hell, where they shared a cell together.
I think sometimes I should.ve moved into the cell beside yours in Hell.
The human had spent most of the evening pacing around the cell, trying to make some sense of everything, stopping only briefly to eat, in an effort to soak up all the alcohol.
Some workers regard certain appearances in dividing cells found in cancer as evidence of a reversion of the somatic cell to the germcell type (heterotypical), otherwise found only in the process which results in the formation of an embryo.
Oertel finds an explanation of this want of complete celldifferentiation, loss of function, and acquired vegetative activity in the non-homogeneous character of the nuclear chromatin elements of the cell, and maintains that the different properties of the cell are carried and handed down by the different orders of chromatin loops.
We have analogies to this in the two nuclei of some of the protozoa, the one being solely for the purpose of propagation, the other being associated with the functional activities of the cell.
If, from whatever cause, any of the chromatin loops belonging to the functional order be lost the descendants of such a cell, being unable to restore these loops, will be minus the functional attributes associated with the lost elements.
The foregoing hypotheses have all sought the origin of new growths in some intrinsic cause which has altered the characters of the cell or cells which gave rise to them, but none of them explain the direct exciting cause.
Autolysis is a disintegration of dead tissues brought about by the action of their own ferments, while degeneration takes place in the still living cell.
There it is acted on by ferments (lipases) and converted into neutral fat, which may remain in the cell as such.
As fat is a food element essential to the carrying out of the vital energies of the cell, a certain amount of fatty matter must be present, in a form, however, unrecognizable by our present microchemical and staining methods.
It can be formed independently of cell activity, nor does it require oxygen.
The liver cells are seen to contain a large globule of fat which pushes the cell nucleus to one side - giving the signet-ring appearance.
Hyaline degeneration is found in certain acute infective conditions; the toxins specially act on these connective-tissue cell elements.
The ovary bears a sessile stigma and is more or less completely two-celled, with two erect ovules in each cell.
A cell when filled with fresh slices becomes the head of the battery, and where skilled scientific control can be relied upon to regulate the process, the best and most economical way of heating the slices, previous to admitting the hot liquor from the next cell, is by direct steam; but as the slightest inattention or carelessness in the admission of direct steam might have the effect of inverting sugar and thereby causing the loss of some portion of saccharine in the slices, water heaters are generally used, through which water is passed and heated up previous to admission to the freshly-filled cell.
When once a cell is filled up and the slices are warmed through, the liquor from the adjoining cell, which hitherto has been running out of it to the saturators, is turned into the new cell, and beginning to displace the juice from the fresh slices, runs thence to the saturators.
When the new cell comes into operation and becomes the head of the battery, the first or tail cell is thrown out, and number two becomes the tail cell, and so the rounds are repeated; one cell is always being emptied and one filled or charged with slices and heated up, the latter becoming the head of the battery as soon as it is ready.
Each cell is of suitable dimensions to turn out a slab of sugar about 14 in.
The ovum first divides into (a) a granular cell, and (b) a cell full of refringent spherules.
Assassins were sent to kill him in his cell; but awed, it is said, by Savonarola's words and demeanour they fled dismayed from his presence.
Mounting his own pulpit in St Mark's he quietly related the events of the day to the faithful assembled in the church, and then withdrew to his cell, while the mob on the square outside was clamouring for his blood.
The prisoners were conveyed to the Palazzo Vecchio, and Savonarola was lodged in the tower cell which had once harboured Cosimo de' Medici.
The vaults are gracefully painted with floreated bands along the ribs and central patterns in each "cell," in rich soft colours on a white plastered ground.
When an alkaline chloride, say sodium chloride, is electrolysed with one electrode immersed in a porous cell, while caustic soda is formed at the cathode, chlorine is deposited at the anode.
Hypochlorites were made, at ordinary temperatures, and chlorates at higher temperatures, in a cell without a partition in which the cathode was placed horizontally immediately above the anode, to favour the mixing of the ascending chlorine with the descending caustic solution.
Similarly, the formation of organic halogen products may be effected by electrolytic chlorine, as, for example, in the production of chloral by the gradual introduction of alcohol into an anode cell in which the electrolyte is a strong solution of potassium chloride.
Accordingly the number of electric cells into which the space round is cut up is equal to twice the energy stored up, or each cell contains half a unit of energy.
The cuticle is secreted by an epidermis in which no cell boundaries are to be seen; it sends out processes into the bristles.
Great numbers of monks, each in solitary cell, spent lonely lives, scorched by the sun, ill-clad and scantily fed, pondering on portions of Scripture or copying MSS.
This monastery was restored in the reign of Robert Bruce, and became a cell of the abbey of canons regular at Inchaffray.
Such, for instance, were those of Spindler and Wrangell in the Black Sea by sinking an electric lamp, those of Paul Regnard by measuring the change of electric resistance in a selenium cell or the chemical action of the light on a mixture of chlorine and hydrogen, by which he found a very rapid diminution in the intensity of light even in the surface layers of water.
A small brook named Barri runs here into the sea, whence the place was formerly known in Welsh as Aber-Barri, but the name of both the river and the island is supposed to be derived from Baruch, a Welsh saint of the 7th century, who had a cell on the island.
The central authorities, which as early as the 18th century worked together in a common mother cell of the State chancery, became differentiated so soon as the growing tasks of administration called for specialization; in 1869 there were seven departments, and in the concluding decade of the Austrian Empire there were set up Ministries of Labour, Food, Public Health and Social Care.
Returning to his cell he continued a labour in which he had been engaged, the transcription of the Psalter.
It consisted of a glass vessel, containing a solution of sulphate of zinc, in which were placed two plates of pure amalgamated zinc. These plates were connected by means of a german-silver shunt, their size and the distance between them being so adjusted that about ii 0 - 0 - part of the current passing through the meter travelled through the electrolytic cell and -j o i j of the current passed through the shunt.
The shunted voltameter was then inserted in series with the electric supply mains leading to the house or building taking electric energy, and the current which passed dissolved the zinc from one plate and deposited it upon the other, so that after a certain interval of time had elapsed the altered weight of the plates enabled the quantity of electricity to be determined from the known fact that an electric current of one ampere, flowing for one hour, removes 1.2533 grammes of zinc from a solution of sulphate of zinc. Hence the quantity in amperehours passing through the electrolytic cell being known and the fraction of the whole quantity taken by the cell being known, the quantity supplied to the house was determined.
To prevent temperature from affecting the shunt ratio, Edison joined in series with the electrolytic cell a copper coil the resistance of which increased with a rise of temperature by the same amount that the electrolyte decreased.
Only the two gran it will take to put the lines down this way, and cell phone reception is unreliable.
Rhyn left the cell block to Toby's protests and walked with Gabe through the antechamber and into the hallway on the other side. Gabe's gaze was dark, his air brooding. Rhyn opened a portal, and they crossed through to Gabe's cabin in the underworld.
Toby felt almost as distraught at having to stay in the cell while his human was lost in the underworld. Not that he didn't trust Rhyn or Gabe, just that, he might be able to find her first.
As Toby watched, Ully stuck his hand out of the cell and placed it on the wall.
His cell door clicked open. Toby bounced to his feet.
Ully returned a couple of minutes later. He strode to Toby's cell and dangled the talisman before it. Toby's door opened.
Toby stepped out of the cell and closed it.
He heard Hannah crying and smelled the unmistakable scent of human blood before he took a step onto the block. He strode down the block and paused in front of Hannah's cell. She was curled up on the bed, sobbing. When he looked at the cell across from her, he saw why. Jared stood in the cell, covered in blood. The cell looked as if a human had exploded, and Rhyn saw a pile of bones Jared had gnawed clean then stacked neatly.
He placed the talisman on the door frame of Hannah's cell. The door opened.
Rhyn ignored the demon and left the cell block, returning to the hallway before opening a portal. He crossed through the shadow world to the beach of the Caribbean Sanctuary. Toby was dragging Kiki up the beach by one leg.
I'm not used to having a phone in the house, much less carrying a cell phone.
Her cell phone was in her pocket, but Alex probably figured she didn't have it with her.
Do you have your cell phone with you?
She took her time getting home, ignoring her cell phone when it rang.
He was probably upset that she didn't answer her cell phone, but he had given her strict orders not to use it when she was driving.
She had forgotten her cell phone on the dresser again.
Ten O'clock found her hanging over the telephone, her cell phone on her hip.
She threw her cell phone on the bed.
If she hadn't thrown her cell phone on the bed, she could have called him.
Can I borrow your cell? she asked.
Sofi had taught him to use his cell phone and Dusty had taught him the computer.
She pocketed the cell, grateful for his consideration.
There were no weaknesses to the cell.
Sofi appeared relaxed in the cell, her head resting against the wall and her brilliant eyes focused on Jenn.
In order to find her, the first guardsmen would have to enter the cell.
Another fell, and the third shoved her into the cell.
She strained to keep her hold on the guardsman, even as the other one left the cell and snatched a sword to finish her off.
Returning to the cell, she used the long-sleeved shirt to wipe the blood off her body quickly and then to clean the blades of the weapons she snatched off the ground.
The heavy, musty scent of earth was contained within a four-by-four-foot cell, not even large enough for him to lie down.
Before she fell again for Sirian's lies, she pushed the lever to seal his cell and walked away, rage and confusion making her head spin.
The iron wall was open in front of Sirian's cell.
The cell holding Sirian was closed.
Hilden caught up to them as they reached the dungeon, where Vara was opening the iron door to the cell containing Sirian.
Memon ignored him, darting into the cell where the unconscious Rissa lay.
Vara hurried to close the iron door while Hilden rushed to the cell holding Memon.
Vara pulled her body towards him until she cleared the cell then lifted her.
Both cell doors had exploded off the cells and lay crumpled across the room.
Memon's lifeless body was wedged between the bars of one cell.
I gave him your cell phone number.
Their lovemaking lasted only a few minutes before his cell phone rang.
Did you know Jonathan told our twins that Alex wants to get him a cell phone but you're being a … unreasonable about it?
Jonathan had reached puberty in full rebellion, which was one of the reasons she didn't think he should have a cell phone.
Fortunately Morino saw the ad for Apple Hors Devours in the local paper and recognized Alfonso's cell phone number before they made their first sale.
Alfonso lost the use of his cell phone for a month and Alex grounded Jonathan for the same amount of time.
That evening at home they were eating supper when Jonathan again asked Alex if he could get a cell phone.
They had badgered the parents of their thirteen year old member into getting him a cell phone and then had started on Carmen.
Later Carmen and Alex had explained to Jonathan that he was too young for the responsibility of a cell phone.
Pulling the cell phone from the holster on her side, she called Felipa.
Alex would be upset, but even worse; it would give Jonathan ammunition in his battle for a cell phone.
Remembering her cell phone, she reached for it.
She might as well figure on getting that cell phone for Jonathan.
Monday morning while Felipa took the men riding and the children were coloring, Carmen used her new cell phone to call the employment office.
If I had a cell phone, I could call you when I was ready.
Her cell phone rang at the exact time she was certain that her head would burst.
Pulling the cell phone from her purse, she tried calling Mr. O'Hara.
Apparently the area where the cabin sat was a dead spot for cell phones.
Another cell could develop at any time and this could start again all over.
This time her cell phone worked and a deep voice answered.
Once again she tried the cell phone, with the same results.
Brandon shoved a hand between the cushions and fished out the cell.
Brandon peppered her with questions, until she finally gave him her cell and let him listen to the messages.
An iPad in a bright green case and a cell phone labeled work phone!!!!! was sitting on the table in the informal dining area, a sticky note on it.
Rule five, keep your cell on.
The work cell rang, and she picked it up, answering instinctively.
I'll give you my cell number.
When you feel like venting, call, Gerry said and picked up her cell.
She fished the cell out of her purse and frowned.
Suddenly, she smiled and grabbed her cell phone.
I GPS tagged my cousins' cell phones and wallets.
Yeah. Only it wasn't just your cell and wallet.
A text drew her attention to the cell phone.
Xander tossed him the cell, and Darian strode out of the barn.
Making sure she's not sneaking up behind me to kill me, Xander said and removed his cell from his jeans.
Several were in Southern California while two blue dots – the one in her cell phone and the other in a shoe – appeared on the map in Texas.
Heart pounding hard, she sat on the bed and pulled out her cell phone.
He took Jessi's arm then whipped out his cell with his free hand.
Traube (1858), the active cause of fermentation is due to the action of different enzymes contained in yeast and not to the yeast cell itself.
He agreed with Pasteur that the presence of living cells is essential to the transformation of sugar into alcohol, but dissented from the view that the process occurs within the cell.
This investigator held that the decomposition of the sugar molecules takes place outside the cell wall.
This body is being continually formed in the yeast cell, and decomposes the sugar which has diffused into the cell.
In this respect the plasma behaves in a similar manner towards the sugars as does the living yeast cell.
He emphasized the opinion that yeast derived from one cell was of no good for top fermentation, and advocated Pasteur's method of purification.
In the United Kingdom the employment of brewery yeasts selected from a single cell has not come into general use; it may probably be accounted for in a great measure by conservatism and the wrong application of Hansen's theories.
The flasks were then well shaken, and the yeast cell or cells settled to the bottom, and gave rise to a separate yeast speck.
To obtain an absolutely pure culture with certainty it is necessary, even when the gelatin method is employed, to start from a single cell.
Fermentation now includes all changes in organic compounds brought about by ferments elaborated in the living animal or vegetable cell.
In most cases four spores are formed within the cell by free formation.
In a monastery at Naples, near the cathedral of St Januarius, is still shown a cell in which he is said to have lived.
In some species (Ascaris decipiens) the giant cell is replaced by an irregular mass of protoplasm containing a number of small nuclei.
Each cell contains a zinc plate, immersed in a solution of zinc sulphate, and also a porous chamber containing crystals of copper sulphate and a copper plate.
The electromotive force of each cell is i 07 volts and the resistance 3 ohms. The Fuller bichromate battery consists of an outer jar containing a solution of bichromate of potash and sulphuric acid, in which a plate of hard carbon is immersed; in the jar there is also a porous pot containing dilute sulphuric acid and a small quantity (2 oz.) of mercury, in which stands a stout zinc rod.
The electromotive force of each cell is 2.14 volts, and the resistance 4.
The size of the accumulators employed varies from a cell capable of an output of 8 ampere-hours, to a size giving 750 ampere-hours.
A totally reflecting prism placed inside the glass cylinder projects the light which penetrates the film upon a selenium cell situated at the end of the cylinder.
To eliminate the sluggish action of the selenium transmitter a selenium cell similar to that at the transmitting station is arranged at the receiving apparatus, and exposed to precisely similar variations of light, the arrangement being such that the lag of this cell counteracts the lag of the transmitting cell.
When such a tube is inserted in series with a single voltaic cell and galvanometer it is found that the resistance of the tube is nearly infinite, provided the filings are not too tightly squeezed.
On creating an electric spark or wave in the neighbourhood of the tube the resistance suddenly falls to a few ohms and the cell sends a current through it.
At the receiving station Marconi connected a single voltaic cell B 1 and a sensitive telegraphic relay R in series with his tube of metallic filings C, and interposed certain little coils called choking coils.
In series with the tube is placed a single voltaic cell and a telegraphic relay, and Marconi added certain coils placed across the spark contacts of the relay to prevent the local sparks affecting the coherer.
In later improvements the secondary circuit of this jigger was interrupted by a small condenser, and the terminals of the relay and local cell were connected to the plates of this condenser, whilst the sensitive tube was attached to the outer ends of the secondary circuit.
This increases the resistance of the electrolytic cell.
If, however, one electrode of this cell is connected to the earth and the other to a receiving antenna and electric waves allowed to fall on the antenna, the oscillations passing through the electrolytic cell will remove the polarization and L temporarily decrease the resistance of the cell.
The receiving arrangements comprised also an open or antenna circuit connected directly with a closed condenser-inductance circuit, but in place of the spark gap in the transmitter an electrolytic receiver was inserted, having in connexion with it as indicator a voltaic cell and telephone.
It is largely used for the purpose of making standard electric cells, such for example as the Weston cell.
He sometimes held the carbon powder against the diaphragm in a small tr ans' shallow cell (from a quarter to half an inch in diameter and about an eighth of an inch deep), and sometimes he used what he describes as a fluff, that is, a little brush of silk fibre with plumbago rubbed into it.
A large nematocyst, with everted thread, is seen in the right-hand ectodermal cell.
The cnidoblasts are the mother-cells of the nematocysts, each cell producing one nematocyst in its interior.
A further stage in evolution is that the muscle-cells lose their connexion with the epithelium and come to lie entirely beneath it, forming a sub-epithelial contractile layer, developed chiefly in the tentacles of the polyp. The of the evolution of the ganglioncells is probably similar; an epithelial cell develops processes of nervous nature from the base, which come into connexion with the bases of the sensory cells, with the muscular cells, and with the similar processes of other nerve-cells; next the nerve-cell loses its connexion with the outer epithelium and becomes a sub-epithelial ganglion-cell which is closely connected with the muscular layer, conveying stimuli from the sensory cells to the contractile elements.
The uppermost is a purely muscular cell from the sub-umbrella; the two lower are epidermo-muscular cells from the base of a tentacle; the upstanding nucleated portion forms part of the epidermal mosaic on the free surface of the body.
If the germ-cells are undifferentiated, the offspring may arise from many cells or from a single cell; the first type is (4) germinal budding, the second is (5) sporogony.
The spore-cell multiplies by division, while the enveloping cell is nutrient and protective.
The spore cell gives rise to a " sporelarva," which is set free in the coelenteron and grows into a medusa.
In Hydra the odcyte is a large amoeboid cell, which sends out pseudopodia amongst the odgonia and absorbs nutriment from them.
The result of cleavage in all cases is a typical blastula, which when set free becomes oval and develops a flagellum to each cell, but when not set free, it remains spherical in form and has no flagella.
Thallophyta are the most lowly organized plants and include a great variety of forms, the vegetative portion of which consists of a single cell or a number of cells forming a more or less branched thallus.
The male gametophyte is represented by one or few cells and, except in a few primitive forms where the male cell still retains the motile character as in the Pteridophyta, is carried passively to the macrospore in a development of the pollen grain, the pollen tube.
The male gametophyte is sometimes represented by a transitory prothallial cell;, the two male cells are carried passively down into the ovary and into the mouth of the ovule by means of the pollen-tube.
The female gametophyte is extremely reduced; there is a sexual apparatus of naked cells, one of which is the egg-cell which, after fusion with a male cell, divides to form a large siispensorial cell and a terminal embryo.
The term Anatomy, originally employed in biological science to denote a description of the facts of structure revealed on cutting up an organism, whether with or without the aid of lenses for the purposes of magnification, is restricted in the present article, in accordance with a common modern use, to those facts of internal structure not concerned with the constitution of the individual cell, the structural unit of which the plant is composed.
An account of the structure of plants naturally begins with the cell which is the proximate unit of organic structure.
The cell is essentially an individualized mass of protoplasm containing a differentiated protoplasmic body, called a nucleus.
A, Cell (individual) of the unicellular Green Alga Pleurococcus, as an example of an undifferentiated autonomous assimilating cell.
The primitive cell sends colorless tubelets (rhizoids, rh.) into the mud on which it grows.
The basal cell has less chlorophyll than the others, and is expanded and fixed firmly to the rock on which the plant grows by the basal surface, rh, thus forming a rudimentary rhizoid.
In such cases the characters of the adult tissue clearly depend solely upon the characters of the cell-walls, and it is usual in plant-anatomy to speak of the wall with its enclosed cavity as the cell, and the contained protoplasm or other substances, if present, as cell-contents.
Note thick walls and oblique slit-like pits with opposite inclination on the two sides of the cell seen in surface view.
It is from such a living and assimilating cell, performing as it does all the vital functions of a green plant, that, according to current theory, all the different cell-forms of a higher plant have been differentiated in the course of descent.
The cells Cell and are commonly joined end to end in simple or branched Tissue filaments.
In the group of the Siphoneae both these types of differentiation may exist in the single, long, branched, tube-like and multinucleate cell (coenocyte) which here forms the plant-body.
In Caulerpa the imitation of a higher plant by the differentiation of fixing, supporting and assimilating organs (root, stem and leaf) from different branches of the single cell is strikingly complete.
Each branch grows simply by the transverse division of its apical cell.
The cells belonging to any given thread may be recognized at an early stage of growth, because each cell is connected with its neighbors belonging to the same thread by two depressions or pits, one at each end.
Many of the lower forms of Brown Seaweeds (Phoeophyceae) have a thallus consisting of simple or branched cell threads, as in the green and red forms. The lateral union of the branches to form a solid thallus is not, however, so common, nor is it carried to so high a pitch of elaboration as in the Rhodophyceae.
In the Fucaceae, on the other hand, there is a single prismatic apical cell situated at the bottom of a groove at the growing apex of the thallus, which cuts off cells from its sides to add to the peripheral, and from its base to add to the central permanent cells.
The whole of the tissue of the plant is formed by the division of this apical cell.
In addition to the cell types described, it is a very common occurrence in these bulky forms for rhizoid-like branches of the cells to grow out, mostly from the cells at the periphery of the medulla, and grow down between the cells, strengthening the whole tissue, as in the Rhodophyceae.
It always consists of true parenchyma, and is entirely formed by the cutting off of segments from an apical cell.
The latter are plates of green tissue one cell thick, while the stem consists of uniform more or less elongated cylindrical cells.
The whole cavity of the cell is sometimes stuffed with proteid contents.
The end of the cell is slightly swollen, fitting on to the similar swollen end of the next leptoid of the row exactly after the fashion of a trumpet-hypha.
The leaf consists of a central midrib, several cells thick, and two wings, one cell thick.
The simplest type consists simply of a single elongated cell projecting above the general level of the lairs, epidermis.
The whole of the middle lamella or originally formed cell-wall separating one from another disappears before the adult state is reached, so that the walls of the hydroids consist of a framework of lignified bars, with open communication between the cell cavities.
On germination of the seed the radicle first grows out, increasing in size as a whole, and soon adding to its tissues by cell division at its apical growing-point.
In most Pteridophytes there is a single large apical cell at the end of each stem and root axis.
In other cases, again, a group of two or four prismatIl cells takes the place of the apical cell.
Apical cell, p. Wall marking limit between the plerome k, initial segment of root-cap. P and the pleriblem Pb.
The periblem, one cell thick at the apex, produces the cortex, to which the piliferous layer belongs in Monocotyledons; and the plerome, which is nearly always sharply separated from the periblem, gives rise to the vascular cylinder.
When a given initial cell of the cambium has once begun to produce cells of this sort it continues the process, so that a radial plate of parenchyma cells is formed stretching in one plane through the xylem and phloem.
Very soon the single cell gives rise to a chain of cells, and this in.
This is a primal necessity of the protoplast,and every cell gives evidence of its need by adopting one of the various ways in which such need is supplied.
The apparently structureless substance is saturated with it; and if once a cell is completely dried, even at a low temperature, in the enormous majority of cases its life iS gone and the restoration of water fails to enable it to recover.
The process involves the iqter-action of water also, and this, as we have seen, is always present in the cell.
But it is certain that it can only be present in a cell in very small amount at any moment, for an extremely dilute solution acts as a poison to protoplasm.
The formaldehyde at once undergoes a process of condensation oi- polymerization by the protoplasm of the plastid, while the hydrogen peroxide is said to be decomposed into water and free oxygen by another agency in the cell, of the nature of one of the enzymes of which we shall speak later.
As much sugar as is produced in excess of the immediate requirements of the cell is converted into the insoluble form of starch by the plastidsof the chlorophyll apparatus, and is so withdrawn from the sphere of action, thereby enabling the construction of further quantities of sugar to take place.
The presence of too much sugar in solution in the sap of the cell inhibits the activity of the chloroplasts; hence the necessity for its removal.
The idea of an identity of protoplasm does not involve a denial of special powers developed in it in different situations, and the possession of such a power by the vegetable cell is not more striking than the location of the powers of co-ordination and thought in the protoplasm of cells of the human brain.
The material and the energy go together, the decomposition of the one in the cell setting free the other, which is used at once in the vital processes of the cell, being in fact largely employed in constructing protoplasm or storing various products.
The supply of oxygen to a plant is thus seen to be as directly connected with the utilization of the energy of a cell as is that of food concerned in its nutrition.
These include cell walls and the various stored products found in growing cells.
This is evident from the consideration that the growth of the cells is attended by the growth in surface of the cell wall, and as the latter is a secretion from the protoplasm, such a decomposition cannot readily take place unless oxygen is admitted to it.
There is set up at once a certain hydrostatic pressure, due to the turgidity which ensues upon such absorption, and the extensible cell wall stretches, at first in all directions.
The growth or increase of the protoplasm at the expense of the nutritive matter for a time keeps pace with the increased size of the cell, but by and by it becomes vacuolated as more and more water is attracted into the interior.
The growth of the protoplasm, though considerable, is therefore not commensurate with the increase in the size of the cell.
The stretching of the cell wall by the hydrostatic pressure is fixed by a secretion of new particles and their deposition upon the original wall, which as it becomes slightly thicker is capable of still greater extension, much in the same way as a thick band of indiarubber is capable of undergoing greater stretching than a thin one.
The increase in surface of the cell wall is thus duefirstly to the stretching caused by turgidity, and secondly to the formation and deposition of new substance upon the old.
When the limit of extensibility is reached the cell wall increases in thickness from the continuation of the latter of the two processes.
The rate of growth of a cell varies gradually throughout its course; it begins slowly, increases to a maximum, and then becomes slower till it stops.
This may possibly be the cell sap in their interior, which must exercise a slightly different hydrostatic pressure on the basal and, the lateral walls of the cells.
Many experiments point to certain small grains of starch which are capable of displacement as the position of the cell is altered.
The peculiarity of the protoplasm in almost every cell is that it is especially active in the regulation of its permeability by water.
It is the immediate cause of the phenomena of circumnutation, each cell of the circumnutating organ showing a rhythmic enlargement and decrease of its dimensions, due to the admission of more and less water into its interior.
Pythium in seedlingsor to a poison diffusing from cell to cell; in the case of unicellular plantse.g.
Plcotrachelus causes the invaded Pilobolus to swell up, and changes the whole course of its cell metabolism, and similarly with Plasmodiophora in the roots of turnips, and many other cases.
If such a general parasite carries its activities farther, every cell may be killed and the plant forthwith destroyed e.g.
If the attack of a parasite is met by the formation of some substance in the protoplasm which is chemo- tactically repulsive to the invader, it may be totally incapable of penetrating the cell, even though equipped with a whole armoury of cytases, diastatic and other enzymes, and poisons which would easily overcome the more passive resistances offered by mere cell-walls and cell-contents of other plants, the protoplasm of which forms bodies chemotactically attractive to the Fungus.
But even when inside it does not follow that the Fungus can kill the cell, and many cases are known where the Fungus can break throtigh the cells first lines of defence (cell-wall and protoplasmic lining); but the struggle goes on at close quarters, and various degrees of hypertrophy, accumulation of plastic bodies or secretions, discolorations, &c.,, indicate the suffering of the still living cell.
Finally, cases occur where the invaded cell so adapts itself to the presence of the intruder that life in commonsymbiosisresults.
The elementary unit of plant structure, as of animal structure, is the cell.
The Cell Theory.For a general and historical account of the cell theory see CYTOLOGY.
The nucleus was definitely recognized in the plant cell by Robert Brown in 1831, but its presence had been previously indicated by various observers and it had been seen by Fontana in some animal cells as early as 1781.
The cell theory so far as it relates to plants was established by Schleiden in 1838.
He showed that all the organs of plants are built up of cells, that the plant embryo originates from a single cell, and that the physiological activities of the plant are dependent upon the individual activities of these vital units.
It is true that in the unicellular plants all the vital activities are performed by a single cell, but in the multicellular plants there is a more or less highly developed differentiation of physiological activity giving rise to different tissues or groups of cells, each with a special function.
The cell in such a division of labor cannot therefore be regarded as an independent unit.
The simplest cell forms are found in embryonic tissues, in.
The protoplasm of a living cell con.sists of a semifluid granular substance, called the cytoplasm, one or more nuclei, and sometimes centrosomes and plastids.
Very little is known of the finer structure of the cytoplasm of a vegetable cell.
In other forms such as Elodea, Nitella, Chara, &c., where the cytoplasm is mainly restricted to the periphery of the sap vacuole and lining the cell wall, the streaming movement is exhibited in one direction only.
In some cases both the nucleus and the chromatophores may be carried along in the rotating stream, but in others, such as T.Titeila, the chloroplasts may remain motionless iii a non-motile layer of the cytoplasm in direct contact with the cell wall.i Desmids, Diatoms and Oscillaria show creeping movements probably due to the secretion of slime by the cells; the swarmspores and plasmodium of the Myxomycetes exhibit amoehoid movements; and the motile spores of Fungi and Algae, the spermatozoids of mosses, ferns, &c., move by means of delicate prolongations, cilia or flagella cf the protoplast.
They are spherical, oval, fusiform, or rod-like, and are always found in the cytoplasm, never in the cell-sap. They appear to be permanent organs of the cell, and are transmitted from one cell to another by division.
The cell sap contains various substances in solution such as sugars, inulin, alkaloids, glucosides, organic acids and various inorganic salts.
It is probable that most, if not all, the metabolic changes which take place in a cell, such as the transformation of starch, proteids, sugar, cellulose; and the decomposition -of numerous other organic substances which would otherwise require a high temperature or powerful reagents is also due to their activity.
If it is absent, the cell loses its power of assimilation and growth, and soon dies.
HaberIandt has shown that in plant cells, when any new formation of membrane is to take place in a given spot, the nucleus is found in its immediate vicinity; and Klebs found that only that portion of the protoplasm of a cell which contains the nucleus is capable of forming a cell-wall; whilst Townsend has further shown that if the non-nucleated mass is connected by strands of protoplasm to the nucleated mass, either of the same cell or of a neighboring cell, it retains the power of forming a cell-membrane.
This has a strong attraction for basic aniline dyes, and can usually be distinguished from other parts of the cell which are more easily colored by acid anilines.
In multinucleate cells the division of the nucleus is independent of the division of the cell.
It may also take place where rapid proliferation of the cell is going on, as in the budding of the Yeast plant.
The spindle figure is probably the expression of forces which are set up in the cell for the purpose of causing the separation of the daughter chromosomes.
Hartog has endeavoured to show that it can only he formed by a dual force, analagous to that of magnetism, the spindle-fibi es being comparable to the lines of force in a magnetic field and possibly due to electrical differences in the cell.
It is clear, however, that an equal quantitative division and distribution of the chromatin to the daughter cells is brought about; and if, as has been suggested, the chromatin consists of minute particles or units which are the carriers of the hereditary characteristics, the nuclear division also probably results in the equal division and distribution of one half of each of these units to each daughter cell.
The two divisions of the spore mother cell in which the reduction takes place, follow each other very rapidly and are known as Heterotype and Homotype (Flemming), or according to the terminology of Farmer and Moore (1905) as the meiotic phase.
Cell Division.With the exception of a few plants among the Thallophytes, which consist of a single multinucleate cell, Caulerpa, Vaucheria, &c., the division of the nucleus is followed by the division of the cell either at once, in uninucleate cells, or after a certain number of nuclear divisions, in multinucleate cells.
In the Thallophytes the cytoplasm may be segmented by constriction, due to the in-growth of a new cell wall from the old one, as in Spirogyra and Cladophora, or by the formation of cleavage furrows in which the new cell-wall is secreted, as occurs in the formation of the spores in many Algae and Fungi.
In a few cases both among the higher and the lower plants, of which the formation of spores in the ascus is a typical example, new cells are formed by the aggregation of portions of the cytoplasm around the nuclei which become delimited from the rest of the cell iontents by a membrane.
Cell Membrane.The membrane which surrounds the protoplasts in the majority of plants is typically composed of cellulose, together with a number of other substances which are known as pectic compounds.
These layers arc secreted by the protoplasm by the direct apposition of substances on those already in existence; and they may go on increasing in thickness, both by apposition and by the intussusception of particles probably carried in through the protoplasmic fibres, which penetrate the cell-wall as long as the cell lives.
Besides the internal or centripetal growth, some cell-walls are thickened on the outside, such as pollen grains, oospores of Fungi, cells of Peridineae, &c. This centrifugal growth must apparently take place by the activity of protoplasm external to the cell.
In many of the Fungi the non-motile male cell or nucleus is carried by means of a fertilizing tube actually into the interior of the egg-cell, and is extruded through the apex in close proximity to the egg nucleus.
In the Florideae, Lichens and Laboulbenjaceae the, male cell is a non-motile spermatium, which is carried to the female organ.
In Monoblepliaris, one of the lower Fungi, in some Algae, in the Vascular Cryptograms, in Cycads (Zamia and Cycas), and in Ginkgo, an isolated genus of Gymnosperms, the male cell is a motile spermatozoid with two or more cilia.
In the Algae, such as Fucus, Volvox, Oedogonium, Bulbochaete, and in the Fungus Monoblepharis, the spermatozoid is a small oval or elongate cell containing nucleus, cytoplasm and sometimes plastids.
Belajeff regards it as a true centrosome; but this is doubtful, for while in some cases it appears to be connected with the division of the cell, in others it is independent of it.
The eggcell or oosphere is a large cell containing a single large nucleus, and in the green plants the rudiments of plastids.
In plants with multinucleate cells, such as Albugo, Peronospora and Vaucheria, it is usually a uninucleate cell differentiated by separation of the nuclei from a multinucleate cell, but in Albugo bliti it is multinucleate, and in Sphaero plea it may contain more than one nucleus.
The strongest direct evidence seems to be that the nuclear substances are the only parts of the cells which are always equivalent in quantity, and that in the higher plants and animals the male organ or spermatozoid is composed almost entirely of the nucleus, and that the male nucleus is carried into the female cell without a particle of cytoplasm.i Since, however, the nucleus of the female cell is always accompanied by a larger or smaller quantity of cytoplasm, and that in a large majority of the power plants and animals the male cell also contains cytoplasm, it cannot yet be definitely stated that the cytoplasm does not play some part in the process.
Boveri in fact has put forward the view that the chromosomes are elementary units which maintain an organic continuity and independent existence in the cell.
In the Cyanophyceae the contents of the cell are differentiated into a central colorless region, and a peripheral layer containing the chlorophyll and other coloring matters together with granules of a reserve substance called cyanophycin.
In the yeast cell the nucleus is represented by a homogenous granule, probably of a nucleolar nature, surrounded and perhaps to some extent impregnated by chromatin and closely connected with a vacuole which often has chromatin at its periphery, and contains one or more volutin granules which appear to consist of nucleic acid in combination with an unknown base.
The sieve tubes contain a thin lining layer of protoplasm on their walls, but no nuclei, and the cell sap contains albuminous substances which are coagulable by heat.
Protoplasmic Continuity.Except in the unicellular plants the cell is not an independent unit.
He took up his residence in Avila, where he had built a convent; and here he resumed the common life of a friar, leaving his cell in October 1497 to visit, at Salamanca, the dying infante, Don Juan, and to comfort the sovereigns in their parental distress.
The pupal stage is passed in an earthen cell, just beneath the surface of the ground.
All that do not happen to attach themselves to a bee of the genus Anthophora perish, but those that succeed in reaching the right host are carried to the nest, and as the bee lays an egg in the cell the triungulin slips off her body on to the egg, which floats on the surface of the honey.
The violent personalities of a pamphlet entitled Marie Joseph Chenier et le prince des critiques (1844), in reply to Jules Janin, brought him a six months' sojourn in La Pelagic, in the cell just quitted by Lamennais.
Vezhdovsky's figures of Rhynchelmis agree with those of Bergh in showing the backward growth of the nephridium from the funnel cell.
Rarely the nephridium does not communicate with the coelom; in such cases the nephridium ends in a single cell, like the "flame cell" of a Platyhelminth worm, in which there is a lumen blocked at the coelomic end by a tuft of fine cilia projecting into the lumen.
In any case the nephridia which occupy the segments of the body generally are first of all represented by paired structures, the "pronephridia," in which the funnel is composed of but one cell, which is flagellate.
Each renal organ is a sac lined with glandular epithelium (ciliated cell, with concretions) communicating with the exterior by its papilla, and by ce, Cerebral ganglia.
Facing the castle, on the western side of the pill, stand the considerable remains of Monkton Priory, a Benediction house founded by Earl William Marshal as a cell to the abbey of Seez or Sayes in Normandy, but under Henry VI.
Further incursions made by the Danes in 998 and in 1015 under Canute probably resulted in the destruction of the priory, on the site of which a later house was founded in the 12th century as a cell of the Norman abbey of Lysa, and in the decayed condition of Wareham in 1086, when 203 houses were ruined or waste, the result of misfortune, poverty and fire.
During his stay at Manresa, he lived for the most part in a cell at the Dominican convent; and here, evidently, he had severe illnesses.
Klaproth in 1799, is obtained when pure carbon (graphite or charcoal) is oxidized by alkaline permanganate, or when carbon forms the positive pole in an electrolytic cell (Ber., 1883, 16, p. 1209).
Externally is a thin cuticle; this covers the epidermis, which consists of a syncytium with no cell limits.
The most interesting room in the palace is Philip II.'s cell, from which through an opening in the wall he could see the celebration of mass while too ill to leave his bed.
Volta's cell consists essentially of two plates of different metals, such as zinc and copper, connected by an electrolyte such as a solution of salt or acid.
The electromotive force of Volta's simple cell falls off rapidly when the cell is used, and this phenomenon was shown to be due to the accumulation at the metal plates of the products of chemical changes in the cell itself.
Constant cells may be divided into two groups, according as their action is chemical (as in the bichromate cell, where the hydrogen is converted into water by an oxidizing agent placed in a porous pot round the carbon plate) or electrochemical (as in Daniell's cell, where a copper plate is surrounded by a solution of copper sulphate, and the hydrogen, instead of being liberated, replaces copper, which is deposited on the plate from the solution).
He found that the amounts of the substances liberated in each cell were proportional to the chemical equivalent weights of those substances.
In order that the current should be maintained, and the electromotive force of the cell remain constant during action, it is necessary to ensure that the changes in the cell, chemical or other, which produce the current, should neither destroy the difference between the electrodes, nor coat either electrode with a non-conducting layer through which the current cannot pass.
As an example of a fairly constant cell we may take that of Daniell, which consists of the electrical arrangement - zinc zinc sulphate solution copper sulphate solution copper, - the two solutions being usually separated by a pot of porous earthenware.
When the zinc and copper plates are connected through a wire, a current flows, the conventionally positive electricity passing from copper to zinc in the wire and from zinc to copper in the cell.
Thus as long as a moderate current flows, the only variation in the cell is the appearance of zinc sulphate in the liquid on the copper side of the porous wall.
In spite of this appearance, however, while the supply of copper is maintained, copper, being more easily separated from the solution than zinc, is deposited alone at the cathode, and the cell remains constant.
Thus in the Daniell cell the dissolution of copper as well as of zinc would increase the loss in available energy.
Considered thermodynamically, voltaic cells must be divided into reversible and non-reversible systems. If the slow processes of diffusion be ignored, the Daniell cell already described may be taken as a type of a reversible cell.
Let an electromotive force exactly equal to that of the cell be applied to it in the reverse direction.
When the applied electromotive force is diminished by an infinitesimal amount, the cell produces a current in the usual direction, and the ordinary chemical changes occur.
If the external electromotive force exceed that of the cell by ever so little, a current flows in the opposite direction, and all the former chemical changes are reversed, copper dissolving from the copper plate, while zinc is deposited on the zinc plate.
Since the final state of the system would be the same as in the actual processes of the cell, the same amount of heat must give a measure of the change in internal energy when the cell is in action.
Thus, if L denote the heat corresponding with the chemical changes associated with unit electric transfer, Le will be the heat corresponding with an electric transfer e, and will also be equal to the change in internal energy of the cell.
The earliest formulation of the subject, due to Lord Kelvin, assumed that this relation was true in all cases, and, calculated in this way, the electromotive force of Daniell's cell, which happens to possess a very small temperature coefficient, was found to agree with observation.
Thus, the thermal equivalent of the unit of resultant electrochemical change in Daniell's cell is 5.66 - 3.00 =2.66 calories.
An electromotive force is therefore set up in this direction, and, if we can calculate the change in available energy due to the processes of the cell, we can foretell the value of the electromotive force.
If we take as an example a concentration cell in which silver plates are placed in solutions of silver nitrate, one of which is ten times as strong as the other, this equation gives E = o 060 X Io 8 C.G.S.
Nernst, to whom this theory is due, determined the electromotive force of this cell experimentally, and found the value 0.055 volt.
This condition may be realized to some extent in a manner that throws light on the general theory of the voltaic cell.
Thus silver, at one end of the cell in contact with many silver ions of the silver nitrate solution, at the other end is in contact with a liquid in which the concentration of those ions is very small indeed.
The concentration of the simple copper ions is then so much diminished that the copper plate becomes an anode with regard to zinc. Thus the cell - copper I potassium cyanide solution I potassium sulphate solution - zinc sulphate solution I zinc - gives a current which carries copper into solution and deposits zinc. In a similar way silver could be made to act as anode with respect to cadmium.
It is now evident that the electromotive force of an ordinary chemical cell such as that of Daniell depends on the concentration of the solutions as well as on the nature of the metals.
In ordinary cases possible changes in the concentrations only affect the electromotive force by a few parts in a hundred, but, by means such as those indicated above, it is possible to produce such immense differences in the concentrations that the electromotive force of the cell is not only changed appreciably but even reversed in direction.
Any reversible cell can theoretically be employed as an accumulator, though, in practice, conditions of general convenience are more sought after than thermodynamic efficiency.
This drop in the electromotive force has led to the belief that the cell is not reversible.
If we connect together in series a single Daniell's cell, a galvanometer, and two platinum electrodes dipping into acidulated water, no visible chemical decomposition ensues.
If, instead of using a single Daniell's cell, we employ some source of electromotive force which can be varied as we please, and gradually raise its intensity, we shall find that, when it exceeds a certain value, about 1.7 volt, a permanent current of considerable strength flows through the solution, and, after the initial period, shows no signs of decrease.
Many experiments have been made with a view of separating the two potential-differences which must exist in any cell made of two metals and a liquid, and of determining each one individually.
Hence, if we assume that, in the Daniell's cell, the temperature coefficients are negligible at the individual contacts as well as in the cell as a whole, the sign of the potential-difference ought to be the same at the surface of the zinc as it is at the surface of the copper.
Since zinc goes into solution and copper comes out, the electromotive force of the cell will be the difference between the two effects.
On the other hand, it is commonly thought that the single potentialdifferences at the surface of metals and electrolytes have been determined by methods based on the use of the capillary electrometer and on others depending on what is called a dropping electrode, that is, mercury dropping rapidly into an electrolyte and forming a cell with the mercury at rest in the bottom of the vessel.
By both these methods the single potential-differences found at the surfaces of the zinc and copper have opposite signs, and the effective electromotive force of a Daniell's cell is the sum of the two effects.
The chitinous chaetae have their origin in special ectodermal pits, at the base of which is one large cell which is thought to secrete the chaeta, as in Chaetopods.
Therefore and m = v I - 'm of d22 (47) constant cell B21 its object is to produce inside the tube a magnetic field equal and opposite to that due to the earth's magnetism.
The small current required is supplied to the coil from a single dry cell.
It is found that in embryological growth the retinal layer of the central eyes forms as a separate pouch, which is pushed in laterally beneath the corneagen layer from the epidermic cell layer.
On the ether hand, a survey of the facts of cellular embryology which were accumulated in regard to a variety of classes within a few years of Kovalevsky's work led to a generalization, independently arrived at by Haeckel and Lankester, to the effect that a lower grade of animals may be distinguished, the Protozoa or Plastidozoa, which consist either of single cells or colonies of equiformal cells, and a higher grade, the Metazoa or Enterozoa, in which the egg-cell by " cell division " gives rise to two layers of cells, the endoderm and the ectoderm, surrounding a primitive digestive chamber, the archenteron.
The tracing of the exact mode of development, cell by cell, of the diblastula, the coelom, and the various tissues of examples of all classes of animals was in later years pursued with immense activity and increasing instrumental facilities.
Whatever be the ancestral cell from which these cells spring, it is in the bone marrow that we find a differentiation into the various marrow cells from which are developed the mature corpuscles that pass from the marrow into the blood circulation.
The centrosomes which play so important a part in cell division may be found either lying within or at one side of the nucleus in the vegetative condition of the cell.
The whole current supplied to the house flows through an electrolytic cell consisting of a glass tube containing two platinum electrodes; the electrolyte is dilute sulphuric acid covered with a thin layer of oil to prevent evaporation.
In the Long-Schattner electrolytic meter, the insertion of the coin depresses a copper plate or plates into an electrolytic cell containing a solution of sulphate of copper; the passage of the current dissolves the copper off one of the plates, the loss in weight being determined by the quantity of the electricity passed.
To these three characters the Hydrozoa add a fourth which is distinctive of the subdivision of the Coelenterata termed the Cnidaria; that is to say, they always possess peculiar stinging organs known as nettle-cells, or nematocysts (Cnidae), each produced in a cell forming an integral part of the animal's tissues.
On the 12th of May, at Strafford's request, the archbishop appeared at the window of his cell to give him his blessing on his way to execution, and fainted as he passed by.
This district suffered terribly in the famine of 1847, and hundreds of victims were buried in pits in the graveyard adjoining the ruined Cistercian cell of Abbeystrowry, a mile west of the town.
In the Dominican monastery the cell which St Thomas Aquinas sometimes occupied is shown.
The primitive stone-roofed oratory is supposed to have been a hermit's cell.
The term potentiometer is usually applied to an instrument for the measurement of steady or continuous potential difference between two points in terms of the potential difference of the terminals of a standard voltaic cell of some kind, such as a Clark or Weston cell.
In principle the modern potentiometer consists of an arrangement by means of which any potential difference not exceeding a certain assigned value can be compared with that of a standard cell having a known electromotive force.
If then we substitute for the standard cell any other source of electromotive force, we can move the slider into another position in which the galvanometer will show no deflection.
Thus, for instance, if an experiment were made with a Leclanche cell, and if the balancing-point were found to be at 1500 divisions on the scale, the electromotive force would be determined as I 50o volts.
Instead of adjusting in this manner the electromotive force of any form of cell, if we pass any constant current through a known resistance and bring wires from the extremities of that resistance into connexion with the slider and the galvanometer terminal, we can in the same way determine the fall of potential down the above resistance in terms of the electromotive force of the standard cell and thus measure the current flowing through the standard resistance.
The potentiometer and the divided resistance constitute a sort of electrical scaleyard by means of which any electromotive force or difference of potential can be compared with the electromotive force of a standard cell.
A, B, C, D, E, F, Terminals to which standard cell or voltages to be tested are attached.
From the potential terminals of the strip, wires are brought to the potentiometer so as to determine their potential difference in terms of the electromotive force of the standard Clark cell.
A necessary adjunct to the potentiometer is some form of standard cell to be used as a standard of electromotive force.
In the case of the Clark standard cell above mentioned the elements are mercury and zinc separated by a paste of mercurous sulphate mixed with a saturated solution of zinc sulphate.
Other voltaic standards of electromotive force are in use, such as the Weston cadmium cell, the Helmholtz calomel cell, and the standard Daniell cell.
The Clark cell is made in two forms, the board of trade or tubular form, and the H form of cell devised by Lord Rayleigh.
In the Weston standard cell cadmium and cadmium sulphate are substituted for zinc and zinc sulphate; it has the advantage of a much smaller coefficient of temperature variation than the Clark cell.
After the platinum wires have been sealed through the glass, a little aqua regia is placed in the cell legs until bubbles of gas arise from the platinum, when it is thrown out and replaced by a solution of mercurous nitrate.
To prepare the cadmium amalgam, one part of pure cadmium is dissolved in six parts of pure mercury, and the product while warm and fluid is placed in one limb of the cell and warmed, to ensure perfect contact with the platinum wire.
In making the paste, so much cadmium sulphate must be added that a saturated solution of that salt is formed and is present in the cell.
The cell has the electromotive force above stated if the amalgam of cadmium has from 6 to 13 parts of mercury to I of cadmium.
The German investigators seem to have a great preference for the H form of cell, but it is clear that a narrow tubular cell of the British board of trade form not only comes more quickly to the temperature of the water bath in which it is placed, but is more certain to be wholly at one temperature.
In cases when great accuracy is not required, a Daniell cell can be used as a standard of electromotive force.
When so made, the cell has an electromotive force of 1.072 volts and no sensible temperature variation.
A popular legend represents the bishop as descending from the window of his cell by a rope which friends had conveyed to him in a cask of wine.
It was attached to a Benedictine priory, founded about the beginning of the 12th century as a cell of St Albans abbey by William de Albini.
On the following day Eric murdered Nils in his cell with his own hand, and by his order the other prisoners were despatched by the royal provost marshal forthwith.
A Trypanosome always possesses two distinct nuclear bodies, one the trophonucleus, regulating the trophic life of the cell, the other, the kinetonucleus, directing its locomotor activities.
He subsequently founded, near the castle, the Benedictine priory of St John, which he endowed and constituted a cell of Battle Abbey.
This byssus is not homologous with that of other Lamellibranchs, but originates from a single glandular epithelial cell embedded in the tissues on the dorsal anterior side of the adductor muscle.
During the childbearing period of life some of these will be nearing the ripe condition, and if one such be looked at it will be seen to contain one large cell, the ovum, surrounded by a mass of small cells forming the discus proligerus.
Eventually this bulging part is broken up into a series of small portions, each of which contains one germ cell or ovum, and gives rise to a Graafian follicle.
As each genital gland enlarges it remains attached to the rest of the intermediate cell mass by a constricted fold of the coelomic membrane, known as the mesorchium in the male, and the mesovarium in the female.
Lying dorsal to the genital ridge in the intermediate cell mass is the mesonephros, consisting FIG.
The Metazoa all commence their individual existence as a single cell or plastid, which multiplies itself by transverse division.
D, Each of the four segment-cells gives rise by division to a small pellucid cell.
He supposes that all organisms have developed from the simple cell, and that this has its origin by spontaneous generation, to explain which he propounds the " carbon-theory," that protoplasm comes from inorganic carbonates.
To the north of the church, beyond the sacristy (L), and the side chapels (M), we find the cell of the sub-prior (a), with its garden.
H is the garden, cultivated by the occupant of the cell.
As an example, we may refer to the small religious house of St Mary Magdalene's, a cell of the great Benedictine house of St Mary's, York, in the valley of the Witham, to the south-east of the city of Lincoln.
The plan given by Viollet-le-Duc of the Priory of St Jean des Bons Hommes, a Cluniac cell, situated between the town of Avallon and the village of Savigny, shows that these diminutive establishments comprised every essential feature of a monastery, - chapel, cloister, chapter-room, refectory, dormitory, all grouped according to the recognized arrangement.
The generally accepted theory is that it was a pagan altar which some hermit afterwards converted into a cell.
From these observations he drew the natural conclusion that the spermatium was a male, sexual cell.
The Heroult cell consists of a square iron or steel box lined with carbon rammed and baked into a solid mass; at the bottom is a cast-iron plate connected with the negative pole of the dynamo, but the actual working cathode is undoubtedly the layer of already reduced and molten metal that lies in the bath.
The cell is filled up with cryolite, and the current is turned on till this is melted; then the pure powdered alumina is fed in continuously as long as the operation proceeds.
The bath is heated internally with the current rather than by means of external fuel, because this arrangement permits the vessel itself to be kept comparatively cool; if it were fired from without, it would be hotter than the electrolyte, and no material suitable for the construction of the cell is competent to withstand the attack of nascent aluminium at high temperatures.
The individual and collective influence of the several impurities which occur in the product of the Heroult cell is still to seek, and the importance of this inquiry will be seen when we consider that if cast iron, wrought iron and steel, the three totally distinct metals included in the generic name of "iron" - which are only distinguished one from another chemically by minute differences in the proportion of certain non-metallic ingredients - had only been in use for a comparatively few years, attempts might occasionally be made to forge cast iron, or to employ wrought iron in the manufacture of edge-tools.
Delage has distinguished as multiplication those cases in which the new individual arises from a mass of cells which remain a part of the maternal tissues during differentiation, reserving the term reproduction for those cases in which the spore or cell which is the starting-point of the new individual begins by separating from the maternal tissues; but the distinction is inconvenient in practice and does not appear to carry with it any fundamental biological significance.
The fruit consists of a three-celled capsule, covered externally with soft yielding prickles, and each cell develops a single seed.
In many Basidiomycetes minute branches arise below the septa; their tips curve over the outside of the latter, and fuse with the cell above just beyond it, forming a clamp-connexion.
Invisible to the microscope, but rendered visible by reagents, are glycogen, Mucor, Ascomycetes, yeast, &c. In addition to these cell-contents we have good indirect evidence of the existence of large series of other bodies, such as proteids, carbohydrates, organic acids, alkaloids, enzymes, &c. These must not be confounded with the numerous substances obtained by chemical analysis of masses of the fungus, as there is often no proof of the manner of occurrence of such bodies, though we may conclude with a good show of probability that some of them also exist preformed in the living cell.
Although many fungi have been regarded as devoid of nuclei, and all have not as yet been proved to contain them, the numerous investigations of recent years have revealed them in the cells of all forms thoroughly examined, and we are justified in concluding that the nucleus is as essential to the cell of a fungus as to that of other organisms. The hyphae of many contain numerous, even hundreds of nuclei (Phycomycetes); those of others have several (Aspergillus) in each segment, or only two (Exoascus) or one (Erysiphe) in each cell.
Physiologically, any cell or group of cells separated off from a hypha or unicellular fungus, and capable of itself growing out - germinating - to reproduce the fungus, is a spore; but it is evident that so wide a definition does not exclude the ordinary vegetative cells of sprouting fungi, such as yeasts, or small sclerotium like cell-aggregates of forms like Coniothecium.
Fertilized egg with the central uninucleate cell (o) surrounded by the oosphere and the fertilizing periplasm (p).
Under other conditions, of which the temperature is an important one, the nucleus in the yeast-cell divides, and each daughter-nucleus again, and four spores are formed in the mother cell, a process obviously comparable to the typical development of ascospores in an ascus.
The fused cell becomes a sporangium, and in it eight spores are developed.
In certain cases single cells develop parthenogenetically, without fusion, each cell producing, however, only four spores.
In the formation of spores the nucleus of the cell divides, the protoplasm collects round the nuclei to form the spores by free-cell formation; the protoplasm (epiplasm) not used in this process becomes disorganized.
The asci may be derived from the terminal cell of the branches of the ascogenous hyphae, but usually they are derived from the penultimate cell, the tip curving over to form the so-called crozier.
By this means the ascus cell is brought uppermost, and after the fusion of the two nuclei it develops enormously and produces the ascospores.
The female organ is essentially a flask-shaped structure; the neck of the flask growing out as the trichogyne, and the belly composed of an axial carpogenic cell surrounded by investing cells, and with one cell (trichophoric) between it and the trichogyne.
These three elements - trichogyne, trichophoric cell, and carpogenic cell - are regarded as the procarp. The spermatia have been shown by Thaxter to fuse with the trichogyne, after which the axial cell below (carpogenic cell) undergoes divisions, and ultimately forms asci containing ascospores, while cells investing this form a perithecium, the whole structure reminding us essentially of the fructification of a Pyrenomycete.
The various cells of these organisms are connected by large pits which are traversed by thick protoplasmic threads connecting one cell with the next.
The Basidiales are further characterized by the complete loss of normal sexuality, but at some time or other in the life-history there takes place an association of two nuclei in a cell; the two nuclei are derived from separate cells or possibly in some cases are sister nuclei of the same cell.
The two nuclei when once associated are termed" conjugate "nuclei, and they always divide at the same time, a half of each passing into each cell.
Between the nuclear association and the nuclear fusion in the basidium many thousands of cell generations may be intercalated.
The teleutospore puts forth on germination a fourcelled structure, the promycelium or basidium, and this bears later four sporidia or basidiospores, one on each cell.
There we find an association of nuclei either by the fusion of two similar cells as described by Christmann or by the migration of the nucleus of a vegetative cell into a special cell of the aecidium.
Whether B, Formation of the first sporethe association of nuclei in the mother-cell (sm), from the ordinary mycelium takes place basal cell (a) of one of the by the migration of a nucleus rows of spores.
The most cell (z) have arisen.
They have never been found to cause in fection, and they have not the characters of conidia; the large size of their nuclei, the reduction of their cytoplasm and the absence of reserve material and their thin cell wall all point to their being male gametes.
Boniface at length put him in prison for safe keeping; he died in a monastic cell in the castle of Fumone near Anagni on the 19th of May 1296.
The skin consists of a layer of cuticle, easily stripped off, secreted by an ectodermal layer one cell thick.
The excitement was fed by the publication of two or three striking sonnets, instinct with the spirit of liberty, which Garrison inscribed on the walls of his cell.
The mechanical work is obtained by movement resulting from a change, it is supposed, in the elastic tension of the framework of the living cell.
In the fibrils existing in the cell a sudden alteration of elasticity occurs, resulting in an increased tension on the points of attachment of the cell to the neighbouring elements of the tissue in which the cell is placed.
These yield under the strain, and the cell shortens between those points of its attachment.
But the volume of the cell is not appreciably altered, despite the change of its shape, for its one diameter increases in proportion as its other is diminished.
The neuron is described as having a cell body or perikaryon from which the cell branches - dendrites and axon - extend, and it is this perikaryon which, as its name implies, muscle produces lactic acids during activity, it has been suggested that acids are among the "fatigue substances" with which muscle poisons itself when deprived of circulating blood.
The work of Camillo Golgi (Pavia, 1885 and onwards) on the minute structure of the nervous system has led to great alteration of doctrine in neural physi nerve cells, that is to say, the fine nerve fibres - since all nerve fibres are nerve cell branches, and all nerve cell branches are nerve fibres - which form a close felt-work in the nervous centres, there combined into a network actually continuous throughout.
The intricate felt-work has by Golgi been ascertained to be a mere interlacement, not an actual anastomosis network; the branches springing from the various cells remain lifelong unattached and unjoined to any other than their own individual cell.
Each neuron or nerve cell is a morphologically distinct and discrete unit connected functionally but not structurally with its neighbours, and leading its own life independently of the destiny of its neighbours.
But when neurons are linked together it is found that nerve impulses will only pass from neuron A to neuron B, and not from neuron B to neuron A; that is, the transmission of the excited state or nervous impulse, although possible in each neuron both up and down its own cell branches, is possible from one nerve cell to another in one direction only.
The inference is that the "fatigue substances" generated in the muscle fibres in the course of their prolonged contraction injure and paralyse the motor end plates, which are places of synapsis between nerve cell and muscle cell, even earlier than they harm the contractility of the muscle fibres themselves.
The alkaloid curarin causes motor paralysis by attacking in a selective way this junction of motor nerve cell and striped muscular fibre.
It forms the trophic centre of Solidarity the cell, just as the nucleus-containing part of every cell is the trophic centre of the whole cell.
On the other hand, in some neurons, after severance of the axon from the rest of the cell (spinal motor cell), the whole nerve cell as well as the severed axon degenerates, and may eventually die and be removed.
This death of the sheath as well as of the axis cylinder shows that it, like the axis cylinder, is a part of the nerve cell itself.
In addition to the trophic influence exerted by each part of the neuron on its other parts, notably by the perikaryon on the cell branches, one neuron also in many instances influences the nutrition of other neurons.
It seems, especially in the case of the nexus between certain neurons, that the influence, loss of which endangers nutrition, is associated with the occurrence of something more than merely the nervous impulses awakened from time to time in the leading nerve cell.
Although the cell body or perikaryon of the neuron, with its contained nucleus, is essential for the maintenance of the life of the cell branches, it has become recognized that the actual process and function of "conduction" in many neurons can, and does, go on without the cell body being directly concerned in the conduction.
The conduction through the amputated cell branches continues unimpaired for many hours.
This indicates that the conjunction between the conducting substance of the dendrons and that of the axon can be effected without the intermediation of the cell body.
But the proper nutrition of the conducting substance is indissolubly dependent on the cell branches being in continuity with the cell body and nucleus it contains.
Evidence illustrating this nexus is found in the visible changes produced in the perikaryon by prolonged activity induced and maintained in the conducting branches of the cell.
In the myelinated cell branches of the neuron, that is, in the ordinary nerve fibres, no visible change has ever been demonstrated as the result of any normal activity, however great - a striking contrast to the observations obtained on the perikarya.
They similarly possess power to repair and to regenerate their cell branches where these are injured or destroyed by trauma or disease.
Hence during the day the assimilatory processes of these cells are overbalanced by their wear and tear, and the end-result is that the cell attains an atomic condition less favourable to further disintegration than to reintegration.
That phase of cell life which we are accustomed to call "active" is accompanied always by disintegration.
When in the cell the assimilative processes exceed dissimilative, the external manifestations of energy are liable to cease or diminish.
The nerve cell just prior to sleep is still well capable of response to stimuli, although perhaps the threshold-value of the stimulus has become rather high, whereas after entrance upon sleep and continuance of sleep for several hours, and more, when all spur to the dissimilation process has been long withheld, the threshold-value of the sensory stimulus becomes enormously higher than before.
Hering has long insisted on a self-regulative adjustment of the cell metabolism, so that action involves reaction, increased catabolism necessitates after-increase of anabolism.
They lower the external activities of the cells, but do they not at the same time lower the internal, reparative, assimilative activity of the cell that in natural sleep goes vigorously forward preparing the system for the next day's drain on energy?
The mature pollengrain is, like other spores, a single cell; except in the case of some submerged aquatic plants, it has a double wall, a thin delicate wall of unaltered cellulose, the endospore or intine, and a tough outer cuticularized exospore or extine.
Germination of the microspore begins before it leaves the pollen-sac. In very few cases has anything representing prothallial development been observed; generally a small cell (the antheridial or generative cell) is cut off, leaving a larger tube-cell.
The nucellus is a cellular tissue enveloping one large cell, the embryo-sac or macrospore.
In the natural order Rosaceae, the series Querciflorae, and the very anomalous genus Casuarina and others, instead of a single macrospore a more or less extensive sporogenous tissue is formed, but only one cell proceeds to the formation of a functional female cell.
In Dicotyledons the shoot of the embryo is wholly derived from the terminal cell of the pro-embryo, from the next cell the root arises, and the remaining ones form the suspensor.
In many Monocotyledons the terminal cell forms the cotyledonary portion alone of the shoot of the embryo, its axial part and the root being derived from the adjacent cell; the cotyledon is thus a terminal structure and the apex of the primary stem a lateral one - a condition in marked contrast with that of the Dicotyledons.
In two Malayan species of Balanophora, the embryo is developed from a cell of the endosperm, which is formed from the upper polar nucleus only, the egg apparatus becoming disorganized.
The priory was afterwards united as a dependent cell to the abbey of Holyrood.
Spirulina sp. (From Engler and Prantl, Pflanzenfamilien, by permission of Wilhelm Engelman.) or because of the decay of a cell, becomes interrupted by breaking, and the free ends slip past one another.
Fischer has further established the fact that the peripheral mass, which is a hollow sphere in spherical cells, and either a hollow cylinder or barrel-shaped body in filamentous forms, must be regarded as the single chromatophore of the Cyanophyceous cell.
Among other contents of the cell, fatty substances and tannin are known.
Volvox sp., surface view of a single cell showing connexions.
In the simplest case it may consist of a single cell, which may tions occur, and the thallus is more or less the continuous tube from remain free during the whole of the greater part of its t xistence, which the group is named.
Attached to the bottom of pools series of the Confervales, the thallus consists of filaments branched by means of rhizoids, the thallus of Characeae grows upwards by or unbranched, attached at one extremity, and growing almost means of an apical cell, giving off whorled appendages at regular wholly at the free end.
Usually, however, only one of the fusing cells is a zoogamete, the other gamete being a much larger resting cell.
When zoospores come to rest, a new cell is formed and germination ensues at once.
This is in consonance with the facts already mentioned that zoospores germinate forthwith, and that the sexually-produced cell or zygote enters upon a period of rest.
The germination of a zygospore or oospore is effected by the rupture of an outer cuticularized exosporium; then the cell may protrude an inner wall, the endosporium, and grow out into the new plant (Vaucheria), or the contents may break up into a first brood of zoospores.
It is held that in Coleochaete a parenchyma results from the division of the oospore, from each cell of which a zoospore arises.
The zygospore becomes surrounded with its own wall, consisting finally of three layers, the outer of which is furnished with spicular prominences of various forms. In Zygnemaceae there is no dissolution of the filaments, but the whole contents of one cell pass over by means of a conjugation-tube into the cavity of a cell of a neighbouring filament, where the zygospore is formed by the fusion of the two FIG.
In Zygogonium, although no cell-division takes place, the gametes consist of a portion only of the contents of a cell, and this is regularly the case in Mesocarpaceae, which occupy the highest grade among Conjugatae.
The oogonium, seated on a stalk cell, is surrounded by an investment consisting of five spirallywound cells, from the projecting ends of which segments are cut off, constituting the so-called stigma.
In Dictyota, Sphacelariaceae and Fucaceae there is a definite apical cell.