THE LEAF. 



63 



triply compound or decompound \supradecomposita), according to 

 the number of the successive branchings of the petiole. The rami- 

 fication follows the same types as that of the ribs of simple leaves, 

 and exhibits analogous subordinate modifications. 



Pinnate leaves are such as have a rachis bearing sessile or stalked 

 lateral leaflets arranged on the feathered plan. Sometimes there is an 

 odd terminal leaflet, when the leaf is unequally or impari-piimate (fig. 

 100). When there is no end leaflet, the leaf is abruptly or pari-pinnate 

 (fig. 99). Interruptedly pinnate means that the opposite pairs of leaflets 

 are alternately large and small, as in Agrimonia. The pairs of leaflets 

 are sometimes called juga ; and if only one pair exists, the leaf is unijugate 

 (fig. 101) ; if more pairs, multijugate. If the leaflets are not in pairs, but 

 alternate with each other, the leaf is alternipinnate. 



Fig. 105. 

 Fig. 104. 



A bipinnate leaf, the pinnae imparipinnate. A tripinnate leaf, the pinnae imparipinnate. 



Bipinnate leaves are formed when the main petiole bears secondary 

 petioles with distinct leaflets pinnately arranged (figs. 10S-104). Tri- 

 pinnate leaves exhibit an additional (tertiary) series of partial petioles 

 with distinct leaflets (fig. 105). When the division goes beyond the third 

 degree, the leaves are called decompound (fig. 106) ; but it is more common 

 to find bipinnate or tripinnate leaves with their leaflets pinnatifid, 

 -partite, &c. 



Palmate (or digitate) leaves are such as have a number of distinct 

 leaflets arising from one point, like the ribs of a simple leaf when the 

 plan is palminerved. Si- or tripalmate leaves are very rare (Araliacese). 

 The only modification appears to be the pedate leaf, analogous to the 

 pedatisect simple leaf, but with distinct leaflets (fig. 107). 



The terms ternate, quinate, and septenate are often applied to palmate 

 leaves with a definite number of leaflets. Ternate leaves, however, may 

 occur either on the palmate (fig. 108) or pinnate plan ; if on the latter, 



