LEAVES. 
Leaves are those organs of plants especially adapted 
to expose large surface areas to light and the atmosphere. 
They are borne on stems. 
Review the work already done on leaves which grew 
on the several plants raised in the laboratory under 
exp. I, and also the work done on buds. From what 
plant structure do leaves develop? Into what two large 
classes may leaves be put? What is the relation be- 
tween the venation of leaves and the number of coty- 
ledons in the seeds from which they develop? 
Leaves are usually composed of two parts, a slender, 
more or less elongated portion called petiole; and an ex- 
panded portion called the blade. Can you find any leaves 
without petioles; any without blades? In addition to 
the two parts above mentioned, leaves often have more 
or less leaf-like expansions at the base of the petioles, 
called stipules. Note the stipules on geranium leaves, 
pea leaves, and others. Do you find stipules in very 
young leaves? What is their function in buds? In some 
leaves (bean e. g.) the proximal end of the petiole is 
modified into a sort of cushion, called a pulvinus. The 
pulvini are functional in leaf movements. 
Netted veined leaves may be either palmately or pin- 
nately netted veined. As an example of the former, we 
will study the maple leaf. What is the general shape of 
the blade of a maple leaf? Is its border smooth? How 
