THE NUTRITIVE ORGANS OF PLANTS 57 



2. Examine the material left after removing the epi- 



dermis, scraping it with a knife. This inner 

 region of the leaf is known as mesophyll (Greek, 

 meso = middle -j- phullon = leaf). Describe the 

 mesophyll, stating how it differs from the epi- 

 dermis. 



3. Look carefully for veins in the mesophyll. Describe 



their appearance. 



4. (Optional.) Make a diagram at least half an inch in thick- 



ness of a small portion of the cross section of the leaf 

 you are studying, labeling upper epidermis, mesophyll, 

 veins, and lower epidermis. 



C. Microscopical structure of leaves. Demonstration. 



1. Strip off a piece of epidermis from one of the thick 

 leaves named in B above ; lay it on a glass slide, 

 add a drop of water, and cover with a cover glass. 

 Examine with the low power of the compound 

 microscope, comparing the specimen with Fig. 

 21. Notice the shape of the cells of which the 



guard-cells sur- 

 rounding a 



cells of epider- 

 mis 



FIG. 21. Lower epidermis of a leaf. (Strasburger.) 



epidermis (shown by the faint outlines of their 

 walls) is composed. -Find little oval bodies scat- 

 tered among the cells of the epidermis, each hav- 



