516 CONSERVATIVE ORGANS. [LECT. X. 



stances the petiole and the expansion are in the 

 same plane; the insertion of the footstalk being at 

 that portion of the margin of the expansion, which 

 is regarded as the base of the leaf; but in some 

 instances it is in the centre of the disk, and then 

 the leaf is termed shieldlike (peltatum), 77. The 

 consideration of terms denoting the other inser- 

 tions of the petiole is deferred until we examine 

 the various insertions of the leaf, of which the 

 footstalk is merely a part. 



The term articulation, as applied to the petiole, 

 is intended to denote that it consists of more than 

 one piece, the pieces being generally united by a 

 small intermediate portion, thicker and more 

 spongy than the parts it unites, commonly of a 

 different colour and capable of motion. The pe- 

 tiole of the simple leaf is rarely, although some- 

 times, articulated, as in Citrus aurantium, 74, a. ; 

 and, also, in the majority of Grasses, at that point 

 which separates the real leaf from its sheathing 

 petiole, and which is generally marked on the 

 inner side by a small membranous appendage, 

 which the elder Botanists termed ligula and mem- 

 brana foliorum, but which is now properly con- 

 sidered a stipule. Articulation is very common 

 in compound leaves. It occurs generally at the 

 attachment of the partial to the common pe- 

 tiole, in such leaves as fold together their leaflets 

 during the night; but, in some instances, there is 

 an articulation, also, near the point where the 



