THE STUDY OF LKAVES 23 



Summary of Kinds of Leaves. - - Leaves mark the joints 

 of stems of plants ; they may be alternate when one at a 

 joint, opposite when two at a joint, whorled when over 

 two are arranged around the joint, and clustered when 

 several are together at one side of the joint ; they an- 

 simple when there is but one blade to a leaf and com- 

 pound when there is more than one blade. Compound 

 leaves are divided into pinnate when the blades are 

 attached along the stalk and palmate when they are at 

 the end. Pinnate leaves may be odd pinnate when there 

 is an odd blade at the end and abruptly pinnate when 

 there is no end blade. Pinnate or palmate leaves may 

 be bipinnate or bipalmate if the blades are not reached 

 till there is a second division of the parts ; it is even 

 possible to have them tripinnate or tripalmate, though 

 such a complication is rare among shrubs. (There are 

 two sub-shrubs often cultivated and popularly called 

 spirea, aruncus and astilbe, which have tripalmate 

 leaves). 



Margins of Blades of Leaves. - -The next important dif- 

 ference to be noted is in the edges of blades of all leaves, 

 simple or compound, which may be studied in the four 

 plates in this chapter and the accompanying descriptions. 

 This difference, in such terms as will be easily compre- 

 hended by any one, divides the blades into three classes : 

 (1) entire, where the edge or margin is without regular 

 notches of any kind ; (2) notched or serrated, where there 

 are regular and somewhat saw-toothed notches ; and 

 (3) lobed, where there are a few larger indentations. A 

 lobed blade may have its lobes entire or serrated. 



The more luxuriant or vigorously growing a plant is 

 the more inclined it is to have notches or lobes along the 

 edges of its blades ; in deciding under which class to 

 place a plant do not too closely examine these excep- 

 tional cases of vigor. The younger and the older grow- 

 ing parts of mulberries illustrate these leaf differences 

 with reference to edges of blades. 



