LRCT. VII.] ANATOMY OF STEMS. 339 



muted into alburnum * ; an opinion which was af- 

 terwards supposed to be fully established by the 

 experiments of Du Hamel and of Dr. Hope, and 

 is still maintained by Mirbel^. The first ob- 

 ject of Du Hamel was to ascertain whether the 

 new layer of wood was formed by the bark, or by 

 the former layer of wood. He raised a portion of 

 the bark of a growing tree, and introduced under 

 it a piece of tin foil, over which he carefully bound 

 down the bark ; and, after the wound was healed, 

 allowed the tree to remain in the ground for some 

 years. He then cut it down, and found layers of 

 wood on the outside of the tin foil ; but none had 

 been formed between the foil and the wood with 

 which it had been placed in contact ^. This experi- 

 ment, although it was decisive of the fact, that the 

 new layer of wood is not formed by the old layer 

 which preceded it, yet has been justly objected to 

 by Mr. Knight as by no means confirming the opi- 

 nion of Malpighi regarding the transmutation of 

 the liber into wood; and the same objection may be 

 applied to the following experiment of Dr. Hope, 

 detailed by Sir J. E. Smith, on the authority of his 

 son, Dr. Thomas Hope. " A longitudinal incision 



* Anat. Plantarum. 



f " La transformation du liber en aubier est prouvee par 

 " Tobservation microscopique et par 1'experience." Elemens de 

 Phys. veg. p. 106. 



J Phys. de Arbres, 1. iv. c. 7. 



z 2 



