264 VEGETABLE ORGANOGRAPHY. 



Let us take, in particular, the structure of leaves said 

 to be pinnatisected, palmatisected, or peltisected ; in 

 these the segments have their limb distinct ; but they 

 are attached to the central nerve, or to the top of the 

 petiole, by a nerve which is a division of the petiolary 

 bundle, and continuous with it. Let us suppose now 

 that instead of this continuity, the segment is attached 

 to the petiolary bundle by a true articulation, and we 

 shall have transformed, in thought, this segment into 

 a leaflet, and the simple leaf into a compound one. 

 This difference, although constant in the same species 

 and in certain families, is so slight that it is often diffl- 

 cult to affirm if such partial limb be attached to its base 

 by continuity or articulation ; or, in other terms, whether 

 it be a segment or leaflet, and whether the whole be a 

 simple or compound leaf: this difficulty is especially 

 experienced when the leaves are young ; but when they 

 approach the period of their fall the articulations are 

 easily recognised, as they then have a tendenc}' to disar- 

 ticulate. We are also guided by analogy in this respect, 

 as to foreign plants, of which we may only be able to see 

 dried specimens ; for there are some families where com- 

 pound leaves are frequently found, and others where 

 they never are. 



Compound leaves, classed according to the distribution 

 of the nerves, present corresponding divisions to simple 

 ones : thus, they are said to be Pinnate or Winged 

 when the leaflets are distributed on both sides of a com- 

 mon petiole, like the nerves of penninerved leaves — for 

 example, in Rohinia, Astragalus, 8cc. ; — Palmate, when 

 their leaflets diverge from the top of a common petiole, 

 and in the same direction witli it, like the nerves of 

 palminerved leaves — for example, in the Lupine, Horse- 

 chestnut, &c. ; — Peltate, when their leaflets radiate 

 from the top of a common petiole, but on a different 



