'2 ( J2 ANATOMY OF LEAVES. 



present in the petiole and midrib of all leaves with 

 transverse costse belonging to monocotyledonous plants, 

 but the same general arrangement of the vascular cords, 

 and, consequently, the same structure of the frame 

 work, are seen in all of them. 



The fasciculi in these, as in the other leaves we 

 have examined, consist of spiral and proper vessels ; 

 differing, however, in the relative position of the spi- 

 ral, which, here, in each fasciculus, are placed be- 

 tween two bundles of proper vessels. 



Examining, by the same power of the microscope, 

 a transverse section of one of the larger fasciculi of 

 the midrib of the leaf of Canna indica, we find it to 

 consist of one large, and from 3 to 6 smaller spiral 

 vessels, arranged and relatively connected with the 

 proper vessels in a manner closely resembling the ar- 

 rangement of those in the fasciculi which are found in 

 the stems of White Bryony. 



From these remarks on the vascular system in the 

 leaves of monocotyledonous plants, it is evident that a 

 general character, however, variously modified in ma- 

 ny instances, pervades the whole. The bundles of 

 vessels are distinct ; they run in directions parallel 

 to one another ; and the principal fasciculi are unit- 

 ed by smaller transverse cords or bundles, which, 

 form meshes of a rhomboidal figure, all nearly of the 

 same size in the same leaf. 



LEAVES OF DICOTYLEDONOUS PLANTS. 



Tn these the reticulated structure of the vascular 

 frame work is more complex and varied, than in the 

 leaves of the two natural divisions, already examined. 

 This is evident to the unassisted eye on holding up 

 between it and the light any newly expanded leaf : 

 but it is more beautifully demonstrated in the skele- 

 ton of a full-grown leaf, carefully prepared. We 



