580 CONSERVATIVE ORGANS. [LECT. X. 



Tracing the vascular fasciculi from the petiole 

 into the expansion, in the thin, simple leaves of 

 dicotyledons, we find their divisions, subdivisions, 

 and ultimate ramifications much more diversified 

 and minute than in the leaves of monocotyledons. 

 Whatever may be the origin of these divisions 

 and subdivisions, whether they proceed from one 

 central fasciculus, or from several longitudinal 

 costae, the ramifications become smaller and 

 smaller, owing to a diminution of the number 

 of the vessels which they contain ; but not owing 

 to any diminution of the diameter of the vessels 

 themselves: for, although a principal fasciculus 

 may contain larger and smaller spiral vessels, 

 yet the general comparative magnitude of the 

 vessels, in the smallest fasciculus, is the same as 

 in the largest. This question, therefore, again 

 presents itself: Do the vessels of the leaf inoscu- 

 late and anastomose, or are the smaller fasciculi 

 merely separations from the larger? 



Dr. Grew, as I have already stated, denied 

 that they ever inosculate or anastomose until they 

 arrive at their final distribution. In appealing to 

 nature for a solution of this disputed point, we find 

 Grew's opinion so far correct, that the vascular 

 fasciculi of the costse, which are given off from the 

 midrib, are separations from the petiolar fasciculi 

 in their progress towards the apex of the leaf; and 

 that the fasciculi forming some of the secondary 



