Exogenous Tree. 481 



with. It is easy to conceive that, in any tree, almost any ex- 

 tent of living wood may be formed upon dead wood, in conse- 

 quence of the action of buds, provided a proper medium exists 

 in which the new matter can be formed ; and that, while no 

 cohesion takes place between living and dead matter, the usual 

 cohesion may be renewed as soon as two deposits of living 

 matter come again into contact. In this view the specimen 

 now under consideration will, I think, be found at once a 

 beautiful illustration of the theory of the formation of wood 

 from buds, and an insuperable difficulty in the way of any 

 other theories with which we are acquainted. 



The explanation that might be given of this specimen would 

 be as follows : The poplar, when its principal shoot was four 

 years old, was pruned, the whole of its lateral branches being 

 removed. Between the period of being pruned and the next 

 annual formation of wood, the whole plant died, with the ex- 

 ception of the terminal buds, (perhaps the bark,) and the root, 

 with that part of the stem immediately above it. As soon as 

 the terminal buds were called into action by the usual influence 

 of a vernal atmosphere, they obeyed the ordinary laws of 

 development, sending their roots downwards, under the bark, in 

 the form of wood and liber. These roots did not perish, in con- 

 sequence of there having been a sufficient quantity of moisture 

 between the dead bark and wood to favour their descent ; and 

 the moment they came in contact with the living part of the 

 stem at the ground-line, they united with it exactly in the same 

 way as if no dead matter had intervened. Supposing the bark 

 to have been alive, this descent would have been facilitated. 



A communication once established in this manner between 

 the upper and the lower living portions, the intermediate axis 

 would be speedily inclosed within wood of its own nature, with 

 which it could have no organic connexion, on account of its 

 own previous death, and consequent incapacity of secreting 

 the cambium or matter of cellular organization, by which 

 alone this connexion is maintained. The absence of bark 

 from the surface of the loose axis of this specimen was the 

 necessary consequence of the mode of growth which I have 

 supposed to take place ; by which the whole of the bark, 

 whether living or dead, must necessarily have been pushed 



