CHAPTER XIV 



LEAVES AND FOLIAGE 



188. Leaves may be studied from two points of view 

 — with reference to their function, or what they do ; 

 and with reference to their form, or their shapes and 

 kinds. 



189. FUNCTION. — Leaves, as we have seen, make or- 

 ganic matters from carbon dioxid and water; they respire, 

 throwing off carbon dioxid as waste; they digest the 

 starch, that it may be transported; and they perform 

 other vital activities. Functions which require both lungs 

 and stomach in animals (respiration and digestion) are 

 performed by leaves; and in addition to these functions, 

 they appropriate the carbon of the air (process of photo- 

 synthesis), a work which is peculiar to plants. Any part 

 of the plant, however, may bear chlorophyll and perform 



the functions of leaves. Even aerial 

 roots, as of orchids, are sometimes green. 

 190, The general form and structure 

 of leaves is intimately associated with 

 their function : they are thin and much- 

 expanded bodies, thereby exposing the 

 greatest possible surface to light and 

 air. The position of the leaves usually 

 has relation to light, as we have seen 

 (Chapter VIII). Leaves usually hang 

 in such a way that one casts the least 

 shade on the other ; those die and 



124. Simple leaf. One f^n which havc the Icast favorable po- 

 of the eupatoriums . . 

 or boneseU. SltlOnS. 



(90) 



