352 CONSERVATIVE ORGANS. [LECT. VII. 



augmented. Many important points, indeed, re- 

 lating to the inquiry, and involving other hypo- 

 theses, still remain to be examined ; but these 

 must be deferred until I again bring the question, 

 as it is connected with the general theory of the 

 growth of the vegetable body, under your consi- 

 deration *. The following simple facts, therefore, 



* Although it is unnecessary to load the text with any fur- 

 ther details of the various hypotheses, which have been ad- 

 vanced in explanation of the origin of the annual zones of 

 wood, which increase the diameter of ligneous dicotyledons, 

 yet it may not be improper to give here a slight sketch of that 

 of M. Aubert du Petit Thouars, which has for some years past 

 divided the opinions of the French Botanists. He regards 

 each gem which exists at the axilla of a leaf, as an em- 

 bryon resembling, in some respect, that contained in the seed ; 

 and which, to effect its evolution, draws its nourishment from 

 the succulent parenchyma on the bark on which it is seated, 

 and with which he supposes it to have an immediate communi- 

 cation. As soon as the gem begins to be evolved, it sends 

 down fibres, which our author regards as the roots (veritables 

 racines) of the gem ; and these growing and extending by 

 the organic power (qui, comme I'electricite et la lumiere, 

 semble ne point connoitre de distance), pass down between the 

 wood and the bark from the gem whence they originate to the 

 roots of the tree, taking up, as nutriment (la matiere de leur 

 accroissement), in their passage the viscous fluid, or cambium, 

 which at this season is found between the wood and the bark. 

 The sum of these radical fibres constitutes the new layer of 

 wood, which appears in a concentric circle, owing to the 

 leaves, and consequently the gems, whether they are opposite 

 or alternate, rising on every point of the circumference of the 



