276 
THE LEAF 
A study of its leaves shows how a plant solves many of 
its problems. 
238. Parts of a Leaf. — The main part of a leaf is the blade. 
The petiole (Latin, petiolus, fruit stalk) is the part by which 
it is attached to the twig. This sometimes has small pro¬ 
jections called stipules at the base. 
239. Venation. — The leaf of most plants contains ribs or 
veins which determine its main form and serve to keep it firm. 
Figure 260. — Skeleton of Poplar Leaf. 
Note the epidermis still remaining on 
part of the leaf. Poplar leaves skeleton¬ 
ize very easily. This was picked up on 
the street. 
Figure 261. — Leaf 
of Elm. 
Simple leaf with a 
serrate margin and 
pinnately-netted ve¬ 
nation. Note that the 
leaf is asymmetrical 
at the base. The 
general shape is ovate 
oblong, with a sharp 
apex. 
There are two main types of arrangement of veins. The 
first, that in which there are a few veins of about the same 
size which run side by side without branching from the base of 
the leaf to the tip. These are the parallel-veined leaves found 
in grasses, lilies, and most other monocotyledonous plants. 
In the second type, the netted-veined leaves, a few main veins 
branch and divide, filling the spaces between them with a 
