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 units. 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 



FIG. 3. 



Cell of the meristem, from root 

 apex of corn. 



