ANATOMY OF LEAVES. 297 



rroseopc, we perceive that each fasciculus is com- 

 posed of" spiral and proper vessels, the same which 

 we have already seen to constitute the ribs in the 

 leaves of monocotyledons. 



Tracing the vascular fasciculi from the petiole into 

 the expansion, in the thin, simple leaves, now under 

 consideration, we find their divisions, subdivisions, and 

 ultimate ramifications much more diversified and mi- 

 nute than in the leaves of monocotyledons. What- 

 ever may be the origin of these divisions and subdivi- 

 sions, whether they proceed from one central fascicu- 

 lus, or from several longitudinal costae,. the ramifica- 

 tions become smaller and smaller, owing to a diminu- 

 tion 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 fas- 

 ciculus 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. 

 A question therefore arises, whether the vessels of the 

 leaf inosculate and anastomose, or are the smaller fas- 

 ciculi merely separations from the larger ? 



Dr. Grew denied that they ever inosculate or anas- 

 tomose until they arrive at their final distribution, 

 and we find, indeed, this opinion so far correct, that 

 the vascular fasciculi of the costae, which are given oft' 

 from the midrib, are separations from the petiolar fas- 

 ciculi in their progress toward the apex of the leaf; 

 and that the fasciculi forming some of the secondary 

 costae, also, are separated in a similar manner. But 

 in the smaller ramifications, we perceive that many of 

 the fasciculi are connected with each other at nearly 

 right angles ; and in these instances the vessels are 

 not separations from the larger fasciculi ; but are dis- 

 tinct, and merely applied in a peculiar manner to the 

 sides of those from which they seem to arise ; as can 



