CHAPTER II 
FOLIAGE LEAVES: THE LIGHT-RELATION 
8. Definition. A foliage leaf is the ordinary green leaf, 
and is a very important organ in connection with the work 
of nutrition. It must not be thought that the work done by 
such a leaf cannot be done by green plants which have no 
leaves, as the algae, for example. A leaf is simply an or- 
gan set apart to do such work better. In studying the 
work of a leaf, therefore, we have certain kinds of work 
set apart more distinctly than if they were confused with 
other kinds. For this reason the leaf is selected as an in- 
troduction to some of the important work carried on by 
plants, but it must not be forgotten that a plant does not 
need leaves to do this work ; they simply enable it to work 
more effectively. 
9. Position. It is easily observed that foliage leaves 
grow only upon stems, and that the stems which bear them 
always expose them to light ; that is, such leaves are aerial 
rather than subterranean (see Figs. 1, 75, 174). Many 
stems grow underground, and such stems either bear no 
foliage leaves, or are so placed that the foliage leaves are 
sent above the surface, as in most ferns and many plants of 
the early spring (see Figs. 45, 46, 144). 
10. Color. Another fact to be observed is that foliage 
leaves have a characteristic green color, a color so universal 
that it has come to be associated with plants, and espe- 
cially with leaves. It is also evident that this green color 
holds some necessary relation to light, for the leaves of 
plants grown in the dark, as potatoes sprouting in a cellar, 
