6 MORPHOLOGY OF THE CELL. 



considerable time with corresponding increase of the cell- sap ; not unfrequently 

 it mounts up to a hundred or even a thousandfold the volume of the cell at the 

 time of its formation. During this increase, the contour — the collective form — 

 of the whole cell, commonly undergoes a change ; if it was at first roundish or 

 polyhedral, it may afterwards become elongated, filiform, bag-like, prism- shaped 

 in length or tabular in breadth, many-armed, or branched. The cell-wall may 

 increase very considerably in thickness, and this thickening is usually not uniform ; 

 single spots remain thin, in others the thickened membrane becomes prominent 

 without or within ; strap -shaped prominences, spines, knobs, &c. appear. In the 

 substance of the cell-wall itself, differences also manifest themselves, which result 

 in imparting to it greater firmness, elasticity; or hardness, or, on the other hand, 

 greater softness or pliancy. The protoplasm may, in these processes, decrease more 

 and more in quantity, until at last it forms an extremely thin membrane, which lies 

 so close to the cell-wall that it does not become visible till contraction takes place ; 

 after the completion of the growth of the cell-wall it may even entirefy disappear. 

 But in many other cases the protoplasm increases with the increase in volume 

 of the cell ; it forms a thick- walled sac, the substance of which is endowed with 

 constant motion, while filiform or strap-shaped strings of protoplasm often pass 

 through the sap-cavity of the cell In those cells which appear externally green, 

 certain portions of the protoplasm become separated, and assume a green colouring ; 

 these particles of chlorophyll may appear in the form of bands, stars, or irregular 

 masses ; but they usually form numerous roundish granules, and the particles of 

 chlorophyll always appear as parts of the collective protoplasmic substance of a 

 cell. Sometimes, mixed with the green colouring matter which tinges these por- 

 tions of the protoplasm, are pigments of other colours, red, blue, or yellow (as in 

 Floridese, Oscillatorieae, and Diatomaceae) ; or the particles of chlorophyll assume, 

 through changes in their colouring matter, other tints, mostly yellow or red. 

 Colouring matters may also appear as dissolved in the cell-sap. The other chemical 

 compounds which are formed in extremely large numbers in the cell, are mostly 

 dissolved in the cell-sap ; but many of them assume definite forms ; thus arise 

 granules of fat, drops of oil, and frequently true crystals or crystalline bodies. 

 One of the commonest granular compounds present in almost all plants, with the 

 exception of Fungi and some Algae and Lichens, is Starch, the grains of which 

 often accumulate in the cell in numbers greatly exceeding all other substances. 



The most perfectly developed form of cells is found in certain families of Algse, 

 the Conjugatae, Siphoneae, and Diatomaceae. Since in these cases one and the same 

 cell unites in itself the organs for all vegetative functions, and at the same time a 

 many-sidedness in the phenomena of life presents itself, the whole cell attains a high 

 degree of differentiation ; the separate parts, — the cell-wall, the protoplasmic body, and 

 its contents, — show a variety of structure which does not occur elsewhere concurrently 

 in the different parts of one and the same cell. Hence it happens that the same cell has 

 in these cases often to go through the most diverse metamorphoses, so that besides its 

 manifold development as to size, it also undergoes a series of temporary changes of form. 

 Hence these forms of Algae become of great importance for an accurate comprehension 

 of the nature of the cell. (Book 4 1. Algae.) But above all, these cells are distinguished 

 by this, — that, after they have attained the highest grade of development, they are in a 

 condition to divide and to multiply, and at length, sooner or later, give up their 



