242 LEAVES 
from the fact that the edges of the leaves, as viewed from above, 
fit together like the little tiles of a real mosaic. The fitting 
together in this way is the best arrangement for the individual 
leaves in a large mass to receive light. (Fig. 226.) A general 
mosaic arrangement of leaves may be observed in connection with 
almost every broad leaved plant, but is most noticeable in the 
Ivies where their mosaic of leaves often completely cover the 
surface of a wall. In case of stems exposed to direct light on 
only one side, as the horizontal branches of trees, and stems 
prostrate on the ground or in contact with a support, such as 
Cucumbers, Melons, and climbing vines, the petioles of those 
Fic. 227. — Maple twig, showing mosaic arrangement of leaves. 
leaves on the under side of the stem usually curve so-as to bring 
the blades to the light. For example, in looking up into a tree 
in full foliage, one will notice that the horizontal branches are 
comparatively bare underneath, the leaf blades being displayed 
on the upper side as a mosaic. (Fig. 227.) 
When plants receive light from only one side, as plants grown 
in a room near a window, the entire plant usually bends toward 
the light, thus bringing the leaf blades into a better position for 
exposure. (Mig. 228.) 
General Structure of Leaves 
Although diverse in form and arrangement, foliage leaves 
show much uniformity in structure, being so constructed as to be 
adapted to the function of food-making. In general, they have 
