190 



THE LEAF 



separation has occurred, and the lamina has become divided into a 

 number of distinct secondary blades (Figs. 548, 554, etc.). Leaves of 

 this kind are called £'ompound, and their di\'isions. Leaflets.. 



If the leaflets are themselves compound, the leaf is Decompound. 

 Decompound leaves are spoken of as once compound, twice compound, 

 etc., according to the number of successive di\'isions. Leaflets may be 

 distinguished from leaves by the fact that no buds are found in their 

 axils. Leaflets are subject to the application of the same descriptive 

 terminology as leaves. 



Leaflets of the first di^^sion are called Pinnae, those of subsequent 

 di^•isions, Pinnules. 



The continuation of the petiole passing up among the leaflets, that is 

 the midrib of the compound leaf, is the ^rachis ( 6, Fig. 475). 



JJ0 



Fig-5ii. Palmately compound leaf (.-lesciiZus). 5^8. Palmately trifoliolate Xeai {Trifolium). 549. 

 Pinnately trifoliolate leaf il^espedeza) . 550 and 551. Uniioliolate compound leaves of orange. 



When, as in Fig. 548, the compound leaf has no rachis, its division 



being on the same plan as the lobing of the palmatifid leaf, it i s Palmate, 



or Palmat ely comp ound. TMien the rachis does exist, corresponding to 



the pinna tifid tj-pe (Figs. 549 and 554), the leaf i s ^i n n a te ^r Pinnately 



^C omp ound. ^ 



Before proceeding to define the distinct forms of the two classes, we 

 note that it is not always possible to identify them with readiness. For 

 example, the ancestral form of the leaf of the orange was pinnate, but 

 at the present time we find that only the terminal leaflet remains, 

 there being usually at the base more or less of an indication of the two 

 lateral leaflets which once existed (Figs. 550 and 551). Such a leaf 

 cannot, therefore, be properly designated as simple, and we designate 

 it as a Unifoholate compound leaf. 



Compound leaves with three leaflets, usually designated as Trifolio- 

 late, frequently give us considerable difiiculty in determining whether 



