LECT. VII.] ANATOMY OF STEMS. 349 



a new bark, capable of performing all the func- 

 tions of the original. This fact was first observed 

 by Du Hamel. But Dr. Hope's experiment proves 

 that a similar matter is exuded from the liber, 

 when the bark is detached from the wood ; and 

 Mr. Knight observed that in this case it becomes 

 sooner organized than when it is exuded from al- 

 burnum ; and as we cannot conclude that the new 

 bark is first generated from the former year's al- 

 burnum, and then the new alburnum from this 

 newly formed bark, the only mode of getting over 

 the objection is, by supposing that, under that 

 state of circumstances which as it were obliges 

 the wood to form a new bark, the descending 

 juice from the leaves being impeded in its course 

 downwards through the bark, finds its way into 

 the alburnum in much greater quantity than is 

 required for the ordinary purposes of the plant 

 in that part of its structure ; and the alburnous 

 vessels taking on a retrograde action, it is thrown 

 out in the manner described at different points 

 over the denuded trunk. This opinion is sup- 

 ported by analogy in the animal body, on which, 

 when one organ is destroyed, its function is per- 

 formed by another. We are, therefore, fully war- 

 ranted in adopting Mr. Knight's theory, as far as 

 it maintains that the wood is formed from the 

 proper juice which descends from the leaf through 

 the inner bark ; but, in doing so, there are some 



