570 CONSERVATIVE ORGANS. [LECT. X. 



stems of White Bryony (see fig. 4, A. Plate 8). 

 The arrangement of the vessels, however, in the 

 fasciculi of the expansion differ, in some de- 

 gree, from those of the midrib. Placing a trans- 

 verse section (26.) of one of these fasciculi under 

 the microscope, we find that it is composed of 

 two large tangent spiral vessels (a.) surrounded by 

 firm cellular matter ; and of two small isolated 

 vessels (b.), which are spirals also, situated nearer 

 to the upper disk of the leaf; the one before the 

 other, and, in like manner, surrounded by firm cel- 



lular substance. The proper vessels are collected 

 into two distinct fasciculi ; the largest of which 

 (d.) is on the under disk or back of the leaf, 

 and covered by the cuticle only, while the 

 smallest (c.), which is towards the upper disk, 

 is covered by one layer of cellular substance. 

 In the longitudinal section (27.) made through 

 the centre of the fasciculus, in the thickness of 



