2G6 VEGETABLE ORGANOGRAPHY. 



have one, two, three, &;c. pairs, although this term may 

 then be hardly correct ; hut there are species where the 

 leaflets are so evidently alternate, that we do not venture 

 to employ this term, but are contented then to say that 

 they are alternate, and mention their number. 



In all these classes of compound leaves, the leaflet 

 which is placed at the direct prolongation of the petiole 

 bears the name of the Terminal Leaflet, because it 

 terminates the common petiole ; or of the Middle, or 

 more convenientlv the Odd Leaflet, because there 

 are an equal number on each side of it. It frequently 

 happens that this terminal leaflet remains alone, all the 

 others being wanting: this takes place in the Orange, 

 and several Leguminosse. At first sight these leaves 

 seem to be simple, but they are known by their leaflet, 

 or that wliich appears to be the limb of a simple leaf, 

 being articulated with the top of the petiole : we are 

 also guided in this respect by analogy ; thus, all the 

 family of the Aurantiacese have compound leaves ; and 

 the genus Citrus, to which the Orange belongs, comes 

 under this rule, since the articulation can be seen which 

 separates the terminal leaflet from the bordered petiole. 

 It is also by analogy, and by analogy alone, that we can 

 know whether an unifoliolate leaf belongs, in its primi- 

 tive plan, to pinnate or palmate leaves ; thus, it is 

 likely that the Orange is a pinnate leaf reduced to the 

 odd leaflet, and that the SarcopJujUum (PI. 10, fig. 4) is 

 a palmate leaf reduced to the middle leaflet, for all the 

 analogous species are constituted upon this type. 



It is very frequently remarked that in the same 

 species the leaves at the base of the branches have 

 several pairs of leaflets besides the middle one, whilst 

 in those which are nearer the top the number is so 

 diminished that the upper leaves are sometimes reduced 

 to the terminal leaflet. There is in like manner a 



