18 



Plant Physiology 



that it is difficult accurately to speak of a typical cell. 

 Nevertheless, in the higher plants, those cells which make up 

 the meristem, or growing tissues, possess certain character- 

 istics in common, and they may be considered typical in 

 this restricted sense. All other tissues are derived from 



the meristem, hence its 

 peculiar importance. 



A vegetative cell of 

 the growing root apex 

 of corn (Fig. 3) is 

 more or less isodia- 

 metric in form, often 

 shown as a rectangle 

 or polygon in section. 

 The granular proto- 

 plast, or protoplasmic 

 body, differentiated, as 

 denoted later, may be 

 distinguished in such 

 cases with compara- 

 tive ease. It is closely 

 surrounded by the 

 firm cell-wall which is 

 in general more con- 

 spicuous and serves 

 better than the protoplast to differentiate the limits of the 

 cell uni-ts. The protoplasm is further differentiated into a 

 dense, often rather centrally disposed, spheroidal body, 

 the nucleus, and a less dense but granular enveloping 

 cytoplasm. In the cytoplasm, when the meristem is 

 included within the green tissues, there may also be noted 



: ;.-.-. si'--: ...' . -i j- :.->.-.- v, 



r-^v^ I v ? .. # -V** v<". /XVl 



; ': -. :-* v : -,\ -.-.'"/ : *. *-f .*-' 



s..j "-. (v / \ \ .->t-=- . ; --^'y '-; 



>, . . '-.-'.-: >^ - v . >'--. *',"'' 



FIG. 3. Cell of the meristem, from root 

 apex of corn. 



