THE PLANT BODY 



71 



FIG. 33. Stem of Smilax (Myrsiphyllum). d. leaf-like branch, or claclophyll, situated 

 in the axil of a leaf; I, leaf; ped, flower stalk. (After Bergen.) 



3. Leaf 



Although the leaves of the higher 

 plants exhibit much diversity in 

 form, they agree in their essential 

 features. The fundamental func- 

 tions of leaves are to expose to 

 the sunlight the chlorophyll appa- 

 ratus and to afford a surface for 

 evaporation and the exchange of 

 gases with the environment. Ac- 

 cordingly the principal part of a 

 typical leaf is a broad blade, or 

 LAMINA, which affords the optimum 

 conditions for exposure. The leaf 

 is usually attached to the stem by 

 a stalk, or PETIOLE, which is some- 



FIG. 34. Leaf of a Flowering 

 Plant, showing blade, or lamina, 

 petiole, and two stipules at the 

 leaf base. (From Ganong, after 

 Gray.) 



