518 CONSERVATIVE ORGANS. [LECT. X. 



as compounded, or consisting of distinct parts, in 

 which the divisions of the expansion, however 

 multitudinous they may be, are still parts of the 

 same expansion, inasmuch as they are con- 

 nected by the direct and immediate prolongations 

 of the same petiolei That the leaflets in a true 

 compound leaf are distinct organs, is confirmed 

 by the articulations being conspicuous by anato- 

 my, and by the natural habits of the leaf. The 

 articulations in many leaves are rendered conspi- 

 cuous by a cartilaginous structure ; and in others 

 by a swelling of the partial petiole, at its point of 

 union with the common footstalk, which almost 

 impresses the idea of an artificial attachment: in 

 some instances, however, this is so obscure, that 

 it is by dissection only that the fact can be deter- 

 mined. In a longitudinal section of the petiole of a 

 simple leaf and its ramifications, the vascular 

 bundles distributed to the latter appear merely 

 slips from those of the common petiole; but in a 

 compound leaf we find a peculiar vascular arrange- 

 ment, closely resembling that which occurs in the 

 knotted culm and other articulated stems (see 

 p. 312), marking the place where the vessels of 

 the common petiole apparently terminate, and 

 those of the leaflets commence ; thus demonstrat- 

 ing the individuality of the leaflet. At this point, 

 also, as has been already stated, the leaflets spon- 

 taneously detach themselves from the common 



