THE DIFFEKENTIATION OF THE PLANT-BODY 33 



which, as growth proceeds, become continuous with each 

 other and form a system extending throughout the plant. 

 They can be detected in the root, in the cortex of which 



FIG. 37. PART OF LOWER SURFACE OF A LEAF, SHOWING THREE STOMATA - 

 IX DIFFERENT STAGES OF OPENING. X 300. 



they are conspicuous (fig. 35) ; they may be traced through 

 all the ramifications of the stem, and are seen to form a 

 very prominent feature of the mesophyll of the leaves (fig. 

 36). They communicate with the exterior in all the green 

 parts of the plant, 

 especially the leaves. 

 In the -epidermis of 

 all such parts are 

 small openings known 

 as stomata (figs. 37, 

 38), which are pro- 

 vided with two guard- 



rpll<t hv thp hpViavinnr F IG. 38. SECTION OF LOWER EPIDERMIS OF 

 ' ^ l A LEAF, SHOWING A STOMA. x 300. 



of which the aper- 

 tures can be opened or closed. In those regions of the 

 axis where corky layers cut off the metabolic tissue of the 



