90 ELEMENTARY STUDIES IN BOTANY 



food-manufacture. It must not be supposed that leaves do 

 all the work of food-manufacture, for it is done by any green 

 part of the plant ; but leaves do the most of it because they 

 display the most green tissue. 



The leaves of leafy Liverworts and of Mosses have been 

 spoken of, but those leaves belong to the gametophyte. It 



FIG. 70. Portion of the leaf of a maidenhair fern (Adiantum), showing the forking 



veins. 



is in vascular plants that one meets the first sporophyte 

 leaves ; and they are very different in structure from gameto- 

 phyte leaves. 



An important fact to observe in connection with the leaves 

 of vascular plants is that they are not merely expansions of 

 green tissue, but that through the green tissue there extend 

 " veins " (Fig. 70). These so-called veins are extensions of 

 the vascular system into the leaf, for the xylem carries water 



