THE LEAVES OF VASCULAR P[,ANTS. 269 



even in this case, leaves with two leaflets ought always 

 to be considered as pinnate ones, reduced to a single 

 pair, without a terminal one, or apetiolary prolongation ; 

 thus the genera Hymencea and Bauhinia deserve the 

 name which Linnaeus has given them.* 



It is a rule which appears to me without any real 

 exceptions, although there may be apparent ones, that 

 the leaflets of compound leaves have all the nerves 

 pinnate. The fact is so evident, for the most part, that 

 it is sufficient to express it for any naturalist not to 

 doubt that it is at least generally the case ; the apparent 

 exceptions are, — that sometimes the two lateral and 

 lower nerves may be so large and so near the base as to 

 resemble palmate nerves, and that the lateral distinct 

 leaflets may be united with the terminal one, so as to 

 form together a leaf with several distinct nerves ; this 

 phenomenon merits some details. 



Let us suppose a pinnate leaf, the two superior 

 lateral leaflets of which arise so near the terminal one 

 as to be united with it, and we shall have, as in several 

 Rosaceae, and some Leguminosee, a winged leaf termi- 

 nated by a limb, with three palmate nerves, and 

 frequently with three lobes. As the same thing may 

 take place in a palmate leaf, with three or five leaflets, 

 it is transformed into a leaf, the limb of which will have 

 three or five nerves, and probably three or five lobes. 

 If it take place in abruptly pinnate leaves, the junction 

 is a little more difficult, because the distance between 

 the terminal leaflets is rather greater ; but it also takes 

 place sometimes : thus, on comparing together the 

 different species of Bauhinia, it is difficult not to be 

 persuaded that their limb is formed by the natural 

 junction of the inner borders of the two lateral leaflets ; 



Hymeneea signifies that the leaflets are, as it were, married, and Bau- 

 hinia makes allusion to the two brothers Bauhin, celebrated botanists. 



