VEGETABLE.] HISTOLOGY 11 water. Where the protoplasm contains little water and is very dense, as in some seeds, a higher temperature produces little or no change. A violet colour is given to the protoplasm of young cells by the application first of a concentrated solution of copper sulphate, next washing the preparation carefully to remove all free traces of the copper solution and then applying a solution of caustic potash. Iodine gives a brown colour, sugar solution and sulphuric acid a red ; and dilute caustic potash dissolves protoplasm or renders it perfectly transparent. Carmine and other colouring matters do not colour living protoplasm, but impart a brilliant stain to it when dead. Protoplasm is usually separable into two parts, an inner portion, endoplasm, more or less granular, and an outer more dense layer, the ectoplasm or primordial utricle, which is quite free from granules. A similar layer surrounds the protoplasm of the nucleus. ove- The living protoplasm exhibits movements either when ants, inside a cell-wall or when the protoplasm is free and in the condition of a wall-less or primordial cell. The constant changes in protoplasm must be always accompanied by movements, but these are usually too small to be visible, and it is only in a few cases that the amplitude of the movements renders . them visible. The movements are of four kinds, and are distinguished as rotation, circulation, amoeboid, and ciliary. The first is the movement of rotation, as in Vallisncria, and Anacharis, where the whole protoplasmic sac rotates in the interior of the cell. The second is circulation, where portions only of the Erotoplasm move as indicated by the circulation of the granules ither and thither in the mass, as in the cells of the hairs of Tracles- cantia and the stinging hairs of the nettle. In the third or amce- boid movement whole masses of protoplasm not enclosed in walls change their form and position like the amoeba or white blood cor puscle. These movements have been noticed in the amoeboid and plasmodium stage of the Myxomycctcs or gelatinous fungi. Lastly, a movement of small masses of protoplasm destitute of walls, and having parts of the ectoplasm prolonged to form one, two, or more vibratile cilia is not unfrequent in the zoospores, swarmspores, and spermatozoids of cryptogamic plants. All these movements are de- iieudent on and much influenced by varying external conditions, as ight, heat, presence or absence of oxygen, &c. ell- The cell-wall is a thin, elastic, transparent and colourless a11 - membrane, destitute of visible openings (except in some cells of Sphagnum and in bordered pits), but easily per meated by water and gas. It consists of the carbohydrate cellulose (C r) H 10 O 5 ), isomeric with starch, and in young cells it is present in an almost pure state. During the growth of the cell the protoplasm furnishes material for the increase of the wall in size and thickness, and usually during growth of the wall various chemical and physical changes occur in it. The increase in the size of the cell is rarely quite regular or gene ral, except in free cells as pollen grains and spores ; usually the growth is more or less limited to definite parts of the wall, and the increase in size is accompanied by a marked change in form. Inter- calar growth at a ring-like zone on the cell-wall is seen in the genus (Edogonium, while growth at the apex of the cell is not uncommon in many unicellular algse and in hairs, as well as in the peculiar cells (the hyphfe) of fungi. Growth at several points on the surface of a cell gives rise to the stellate forms seen in the pith of Juncus, and a similar but more limited growth is the cause of the "tyloses," or cellular filling-up of vessels seen in many stems, vine, c. The growth of the cell-wall in thickness may be general or local. Usually it is local, and is either internal (centripetal) or external (centrifugal). Local thick ening gives rise to the production of peculiar markings depending on the different optical effects produced by the thickened and un- thickened parts. Pitted markings are very common, rounded or variously shaped portions of the wall being left unthickened, while the form of the pits, and their special arrangement, either irregularly scattered or spirally placed, give a characteristic appearance to the walls of the cells. Pits are often elongated, and when very much elongated, and extending the whole width of the cell, form scalari- form markings, as seen in ferns. When pits are very narrow, cylindrical, deep, and branching, they form canals. Bordered pits, in which the pit is surrounded by a border, occur in the pines. In other cells the thickening assumes the appearance of rings, spirals, or reticulations, which sometimes become detached from the walls. In some instances, as in the wood of the lime and yew, two kinds of marking occur in one cell. Peculiar modifications of internal thick ening are seeu in the root-hairs of Marc/tuntia, in the cells with cys- tolithes in the leaf of the iudia rubber, and in the pith of Ricinus, &c. External thickening is seen on the surface (cuticle of the epi dermis) of the plant or on free cells, as pollen grains, spores, &c., and produces peculiar and characteristic markings in various plants. By the alternation of more and less watery layers the cell-wall be comes marked by concentric lines or striaj, as if the wall was built up of layers or strata formed one inside the other, which, however, is not the case. A longitudinal striation assuming a ring-like or spiral direction is also met with on the walls of many wood and bast cells, and is, like the stratification just mentioned, due to alternations of more and less watery layers in the cell-wall. The inner layer in the interior of the cell and next thejcontents is always a dense layer rich in cellulose and with littl water, a fact at once negativing the incrustation theory. Stratification can be readily seen in transverse sections of the bast fibres in the leaf of Ifoya, or the bast of the stems of many Asclepiadaccoc ; and the longitudinal striation may be seen in the same fibres when dried, or in the dry wood cells of many conifers, as in Pimis sylvestris. The walls of young cells consist almost exclusively of Reactions pure cellulose, which is coloured blue by Schultz s solution 1 f celm - or by iodine and sulphuric acid, and is dissolved by strong lose> sulphuric acid and by ammoniacal solution of cupric oxide. Iodine solution alone gives no reaction, or more generally a brown tint ; rarely the wall gives a blue reaction, as in the asci of some lichens or in the cells of the cotyledons of Tamarindiis indica. The cell-walls of most fungi do not give a blue reaction with iodine and sulphuric acid, form ing the modification generally known as fungus cellulose. During growth changes occur in the nature of the wall, different strata often having different chemical and physical properties. The three most important changes in the cell- changes wall are (1) the suberous or corky change, the cell- wall in cell- wholly or partially becoming cuticularized or converted into wa ^- cork ; (2) the ligneous or woody change, the walls being converted into wood ; and (3) the gelatinous change, as seen in many algoe, where the cell-wall swells up enormously by the imbibition of water, and assumes a clear gelatinous appearance. These changes may occur separately, the whole wall being more or less completely changed ; or a part remains composed of cellulose ; or, in other cases, two or more of these changes may coexist in the same cell- wall. The following reagents are useful in distinguishing the different changes. Schultz s solution gives a blue with starch and cellulose, and a yellow-brown with wood and cork. If the cork-cells are pre viously boiled in caustic potash, and the wood cells touched with nitric acid, the blue reaction may be got with sulphuric acid and iodine. Sulphuric acid dissolves wood cells, but does not touch cork cells. Ammoniacal solution of cupric oxide docs not dissolve cork, causes wood to swell xip and to become blue, and deeply colours mucilaginous walls. Boiling caustic potash ultimately dissolves cork. Cold caustic potash at first causes it to swell up and become yellow, and when slowly heated the colour deepens and the texture becomes granular. 2 Chlorate of potash and nitric acid (Schultz s macerating fluid) ultimately dissolves cork, like caustic potash, but does not affect wood . When cork-cells are slowly warmed in this mixture the walls of the cork-cells become very distinct, the other cells being very transparent, and, if washed and treated with alcohol and then with ether, they become perfectly transparent. Chromic acid renders cork distinct by rendering other tissues tran sparent. Bichromate of potash dissolves cork. The following re actions are given by Zacharias for cell-walls which are coloured brown by Schultz s solution in the rhizome of Acorns Calamus. 3 Sulphate of aniline and hydrochlorate of aniline, even when the cells are pre viously treated with hydrochloric acid, give no reaction, but colour the walls of vessels of a golden yellow. An aqueous solution of aniline blue gives no reaction, while an alcoholic solution of aniline red colours the walls of vessels and oil-glands. The red colour is 1 Schultzs Solution. 1 ounce of fused chloride of zinc is dissolved in
fluid ounce of water ; then add iodine 3 grains, and iodide of potas
sium 6 grains, dissolved together in the smallest possible quantity of water. Or dissolve granulated zinc in hydrochloric acid, and evaporate in contact with metallic zinc until a thick syrup is formed. Add iodide of potassium to saturation, then a little iodine, and if necessary dilute with water. 2 For this and other reactions see Hohnel, Ueber den Kork und ver- korkte Gewebe ubffrhaupt, p. 16,. 3 "Ueber Secret-Behalter init Terkorktcn Membranen," Lot. ZeUung t
1879, p. G19.
