LEAVES. 67 



the extremity of this tendril is developed Ihe pitcher with u 

 lid closely fitting its orifice. The whole of this curious pro- 

 duction, except the lid, is supposed to be the petiole w hich at 

 first assumes the common form, and afterwards becomes a 

 PhyUodium (as a leaf like expansion of the petiole is called,) 

 and is succeeded hy the tendril, and finally by the cohering 

 of its edges, forms the pitcher, whose lid is the lamina of the 



leaf. 



72. An unusual development of certain parts often pro- 

 duces great variations from the regular form. The petiole is 

 the part of the leaf that experiences most fiequcnt changes 

 from this cause. In the Diona;a Muscipula (fig. Gl,) we 



find the petiole expanded into a phyllodium and terminated 

 by the lamina bearing much less the appearance of this part 

 of the organ than the petiole. The orange also has an ex- 

 panded petiole with t\\e lamina articulated to its extremity. 

 We have described, by authors, foreign plants exhibiting re- 

 markable variations from any regular type, in some of which 

 the petiole is developed apparently at the expense of the la- 

 mina, which is either entirely wanting or but imperfectly de- 

 veloped. The leaves of the onion are supposed to be a devel- 

 opment of the petiole with no lamina, and many of the leaves 

 of the Endognns are supposed to be of the same nature, as the 

 Iris, Calamus, 6ic. The excessive development of the cellu- 

 lar substance in leaves, often causes great diversity in appear- 

 ance as in the various species of the Mesembryanthemums, (Ice 

 plant,) this cause operates to produce the singular forms ob- 

 served in the difierent species of this genus. In the Begonia, 

 the parenchvmous development on one side of the midrib is 



