LECT. X.] ANATOMY OF LEAVES. 561 



in the leaves of the gramineous tribe of plants is, 

 that, in the petiole, the vessels run in distinct fas- 

 ciculi, which are all nearly equal in point of 

 size (14.) ; whereas in the expansion the fasciculi 

 differ considerably in size ( 13.), the larger only 

 being very visible on the surface. In both, there 

 are transverse threads which connect the longitu- 

 dinal bundles, and these are conspicuous even to 

 the naked eye in the more succulent leaves, par- 

 ticularly in those which involve the fructification 

 of the Mays (15.), when viewed by transmitted 

 light. 



In examining a transverse section of a portion 

 of the expansion, of the leaf of Indian Corn, con- 

 taining one of the visible costae and the interval 

 between it and the next costa; we immediately 

 perceive the difference of structure in the two kinds 

 of fasciculi. The visible costa consists of two 

 large spiral vessels on the same line, and a com- 

 pact fasciculus of proper vessels on each side of 

 the line of spirals, towards both surfaces of the 

 leaf (c. c. fig. 13, Plate 10); while, in the interval, 

 each fasciculus is composed of one small spiral ves- 

 sel only, surrounded with a circle of proper ves- 

 sels, and placed in the heart of the substance 

 of the leaf (d. d. d. fig. 13, Plate 10). But, be- 

 sides these, there is another kind of fasciculi, 

 two of which are generally observed in each space 

 between the visible costse, connected with a pe- 



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