MORPHOLOGY 



53 





the cell cavity. This body is the cell NUCLEUS. If sections, made 

 in different directions through the vegetative cone, be compared with 

 one another, it will be seen that its component cells are nearly 

 cubical or tabular, while the nuclei are more or less spherical or 

 disc-shaped. The finely granular substance (cy) filling in the space 

 between the nucleus (k) and the cell wall (m) is the CELL PLASM or 

 CYTOPLASM. In the cytoplasm there are to be found, about the 

 nucleus, a number of colourless and highly refractive bodies : these 

 are the pigment-bearers or CHROMATOPHORES (ch). NUCLEUS, CYTO- 

 PLASM, AND CHROMATOPHORES, CONSTITUTE THE ELEMENTS OF THE 

 LIVING BODY OF A TYPICAL VEGETABLE CELL. To designate all 



these collectively, it is customary to use the term PROTOPLASM, 

 which is then to be understood as including all the living con- 

 stituents of the cell or PROTOPLAST. 



In many animal cells modern investigations have revealed, in 

 addition to the constituents of the protoplasm just mentioned, a 

 small structure situated close to the 

 nucleus, which has been termed the CEN- 



TROSOME, CENTRIOLE, or ATTRACTION- 

 SPHERE. Similar structures have been 

 demonstrated in the lower cryptogamic 

 plants (Fig. 57 c), but they appear to 

 be wanting in the cells of the higher 

 Cryptogams and the Phanerogams ( 31 ). 

 The nucleus and cytoplasm are 

 the two most essential constituents 

 of the cell, and its vital functions de- 

 pend on the interaction between them. 

 In the lowest plants (Cyanophyceaeand KIU. 57. A nucleus <>f u c.-u (l f tu.- ymn- 



Bacteria) such a division of labour in 1>la ", t "' '.'"" x """"-; 1 B " JU ", s " : " 



' . , weed. '//, llio nttToandiBg cytoplasm ; 



the protoplasm IS not certainly proved, ki the nucleus ; kw, nuclear membrane ; 



the existence of a nucleus being still ". nucieoius; .-, ceutrosome; a,, dn-o- 



e j- /Q.}\ /~ir matoi>hores. (x 1000.) 



a matter of dispute ("). Cnroma- 



tophores" are wanting in the Bacteria and Fungi, as in all animal 



cells. 



While animal cells usually remain continuously filled with 

 protoplasm, vegetable cells soon form large SAP CAVITIES. It is only 

 the embryonic cells of plants that are entirely filled with protoplasm, 

 as the cells, for example, of an embryo or of a growing point ; they 

 afterwards become larger and contain proportionally less protoplasm. 

 This can be seen in any longitudinal section through a stem apex. 

 At a short distance from the growing point the enlarged cells have 

 already begun to show cavities or VACUOLES (v in A, Fig. 58) in 

 their cytoplasm. These are filled with x a watery fluid, the CELL SAP. 

 The cells continue to increase in sie, and usually soon attain a 

 condition in which their whole central portion is filled by a single, 



