LECT. X.] ANATOMY OP LEAVES. 557 



the greater number of the circles of the distinct 

 fasciculi, which compose the stems of monocoty- 

 ledons, terminate in leaves until the plant attains 

 its ultimate growth. 



In order to examine properly the vascular 

 framework or skeleton of the petiolated leaves of 

 monocotyledonous plants, we must arrange them 

 under two subdivisions. 1. Those in which the 

 ribs run longitudinally, or in a direction from the 

 base to the apex of the leaf: and, 2. those in which 

 they run nearly transversely, or in a direction 

 from the midrib to the margin. 



1. In this subdivision we perceive that, in the 

 Grasses, the vascular fasciculi resemble, very 

 closely, those of the former division: the ribs 

 being in longitudinal, nearly parallel lines, con- 

 verging towards the apex of the leaf; and united 

 at irregular distances by obliquely transverse 

 threads. If we take a stem leaf of Indian Corn, 

 Zea Mays, as a specimen, we perceive the petiole, 

 which is broad, expanded, and sheathing, deriving 

 its origin from the whole circumference of the 

 knot of the articulation which produces it; dilat- 

 ing gradually as it rises upwards, until its edges 

 become a thin fimbriated membrane, and again 

 contracting, but less gradually, at its upper part, 

 or where it is united to the expansion of the leaf. 

 The vascular bundles, which can be readily traced 

 by the naked eye, are composed of the two distinct 



