40 



BOTANY. 



[CHAP. i. 



and chlorophyll, and becomes divided by a wall formed 

 at right angles to the one previously formed, or parallel 

 to the long axis of the leaf; the two small cells thus 

 formed from the stoma mother-cell are called the guard- 

 cells of the stoma. The common- wall separating the two 

 guard-cells splits, and the guard-cells becoming concave 

 on the side facing each other thus form a small opening 



>Fig. 12. Transverse section through the epidermis of the leaf of 

 Cycas revoluta, one of the Cycads ; n, the elevated epidermis ; e, 

 epidermal cells ; sp, stoma ; c, air cavity below the stoma ; p, paren- 

 chymatous cells of the leaf. (Highly magnified.) 



through the split wall of the epidermis into the substance 

 of the leaf. 



Stomata are most numerous and perfectly developed 

 on leaves, and are either scattered, the most general 

 method, arranged in groups, or, as in the fir-trees, in 

 lines. Their number varies from 200 to 160,000 or even 

 more in a square inch of surface. In the white garden 

 lily there are about 60,000 in a square inch on the under 



