LECT. VJI.J ANATOMY OF STEMS. 34l 



Before, however, entering into the details of Mr. 

 Knight's doctrine, it will be proper to notice that 

 of Dr. Grew, who conceived that a new ring of 

 sap-vessels is first generated in the mucilage 

 thrown out between the bark and the wood, to 

 which he gave the name of Cambium; and this 

 ring of vessels, lining the inner surface of the 

 liber of the former year, is converted into a new 

 layer of liber that ultimately splits into two por- 

 tions, the outer of which forms the new layer of 

 bark, and the inner the new layer of wood. Not- 

 withstanding the inconsistency of this hypothesis, 

 in supposing that the mere separation of the two 

 portions of the liber could produce, in one of 

 these, a new organization and properties, so dis- 

 tinct as those which the wood possesses from the 

 liber, yet it has been characterized, by a late able 

 writer on vegetable physiology, as " perhaps more 

 " conformable to fact" than any other *. Du 

 Hamel made several experiments to ascertain 

 its truth. He passed threads of fine silver wire 

 through the bark of a tree, some near the outer 

 part, or towards the epidermis; others near 

 the liber, others through the liber itself; and 

 others between the wood and the liber. After 



" always very supple with slimy moisture, from which ductile 

 " matter the woody fibres, vesicles and buds are formed." Ve- 

 getable Staticks, p. 340. 

 * Mr. Keith. 



