364 THE BIOLOGY OF THE PLANT 



h. Structure. — Notice that the leaf consists of a stalk, 

 the petiole, which, in the case of simple leaves, 

 bears a single flat expansion, the blade, or, as 

 in compound leaves, several such expansions, 

 the leaflets. Arrange all of your specimens in 

 two groups, putting the simple leaves in one 

 group and the compound in the other. Write a 

 list of the specimens included in each group. 

 Sometimes the petiole bears on its lower end a 

 pair of expansions, the stipules. Make a list of 

 all your specimens which bear stipules, i. e., are 

 stipulate ; another list of the exstipulate 

 leaves. In some cases no petiole is to be found. 

 Make a list of such sessile leaves. 



Study all the leaves with regard to the follow- 

 ing points : 



1. The petiole. — "What is its shape? Length? 



Diameter? Is it marked by a furrow or 

 channel ? If so, on which side of the petiole is 

 it ? What is the nature of the surface of the 

 petiole ? What is the shape of its base ? 



2. The blade or lamina. — Examine first the sim- 



ple leaves. Is the blade in all cases distinctly 

 separated from the petiple ? What is its color ? 

 What is the general shape of the blade ? Does 

 it consist of a single, entire piece, or is it vari- 

 ously lobed ? What is the shape of the apex ? 

 Of the base? Of the margin? What is the 

 texture of the leaf ? Does the lower side differ 

 from the upper ? 



Study the arrangement of the veins (vena- 

 tion) in the blade. At what point do the prin- 

 cipal veins begin ? Do you in all cases find a 

 single large vein or midrib running from the 



