290 ANATOMY OF LEAVES. 



the accompanying compact bundle of proper vessels 

 of the visible costa. In a section obtained by slicing 

 the leaf, we find all these fasciculi united by trans- 

 verse threads, forming rhomboidal meshes, similar to 

 those which have been already described. 



But although the arrangement of the vascular sys- 

 tem of the leaf of Indian Corn, just described, may 

 be taken as a specimen of that peculiar to the leaves 

 of all the Grasses ; and to those leaves of monocoty- 

 ledonous plants which are petiolated, and furnished 

 with longitudinal costae, yet, there must necessarily 

 be many modifications of this arrangement. 



In the leaves of those monocotyledonous plants, 

 the costae of which, instead of being longitudinal, run 

 in transverse parallel lines, forming acute angles with 

 the midrib, we find that the arrangement of the vascu- 

 lar frame work resembles that of the Grasses in some 

 circumstances ; but differs from it in other respects. 

 Thus the costae are parallel to one another, and com- 

 municate by small transverse cords of vessels, so as 

 to form meshes which are rhomboidal or square ac- 

 cording to the angles at which these transverse cords 

 are given off from the costas, as in the Grasses. The 

 petioles are, also, in general, sheathing, and many of 

 them are furnished with ligulae. But, in almost all 

 of them, the peculiar cartilaginous articulation, which 

 divides the petiole from the expansion in the Grasses, 

 is not present; and the petiole assumes a stalk-like 

 aspect before it reaches the expansion. 



Taking the leaf of Carina indica (or Indian shot) 

 as a specimen of the vascular system in this descrip- 

 tion of leaves, we perceive, on the under disk, that 

 the midrib is much elevated near the base, and grad- 

 ually diminishes in size, until it appears little more 

 than a mere line at the apex of the leaf. The more 

 elevated ribs are the primary vascular bundles or fas- 



