342 CONSERVATIVE ORGANS. [LECT. VII. 



some years, when the tree was cut down, those 

 that were placed towards the epidermis were found 

 covered by a thin, decayed, and friable crust 

 only ; those that were placed near the liber were 

 now among the external cortical layers ; those 

 that were passed through the liber were now im- 

 bedded in the wood ; as were those, also, that had 

 been placed between the wood and the liber *. At 

 first sight this experiment appears perfectly con- 

 clusive of the truth of Grew's opinion ; but, when 

 we consider the probability that the wood and 

 the liber are formed at the same time ; for the vi- 

 tal action which is capable of forming the one is 

 undoubtedly equal to the generation of both ; the 

 difficulty of drawing an accurate inference from 

 such an experiment is obvious : and if our reason- 

 ings must be hypothetical, there is certainly more 

 wisdom in deciding in favour of that conjecture, 

 which explains the effect by simple and direct 

 means, than of that which supposes two causes, 

 the one consequent on the other ; and the second 

 involving a difficulty as great as that which it is 

 intended to explain. 



But the true explanation of the phytological 

 fact under consideration, was reserved for Mr. 

 Knight, whose experiments and observations have 

 settled almost every doubt upon the subject. Mr. 

 Knight could not avoid admitting that the ex- 

 periments of Du Hamel and of Dr. Hope were 



* Physique des Arbres t 1. iv. c. 7. 



