566 CONSERVATIVE ORGANS. [LECT. X. 



from the expansion in the Grasses, is not present ; 

 and the petiole assumes a stalk-like aspect before 

 it reaches the expansion. 



Taking this leaf of Canna Indica (21.), as a 



specimen of the vascular system in this description 

 of leaves, we perceive, looking at the under disk, 

 that the midrib is much elevated near the base, 

 and gradually diminishes in size, until it appears 

 little more than a mere line at the apex of the 

 leaf. The more elevated costse (a. a. a. a. a.) are 

 the primary vascular fasciculi ; and between these 

 are secondary fasciculi, which are less elevated. 

 To the unassisted eye they all appear to go off from 

 the midrib ; but viewed by a magnifying lens, and 

 with transmitted light, we perceive that all of 

 them do not proceed directly from the fasciculi of 

 the midrib (22. b. b. see page 567), but that some 

 of them (22. a. a.) are branches of the others*. At 



* In figure 22, the cuticle, except at the space c. d. is taken 

 off, and the midrib pared down, to show the transverse vascular 

 threads, which unite the parallel fascicles ; and which are ren- 

 dered very conspicuous when viewed by transmitted light, 



