LETTER XVI. 



171 



proximity of leaves is not required for the growth of 

 the additional layers of wood and bark into which it 

 developes itself, — nothing else being needed than a 

 supply of elaborated sap which may have been pre- 

 pared by the leaves of remote parts of the fabric." * 

 And in connection with this, let me again remind you 

 of what he says of the leaves — viz. that they are 

 only the most important of the vegetative organs of 

 the plant," — " offsets from the general cellular basis, 

 developed for a particular purpose, the elaboration of 

 nutriment." 



7. Turn now to Letter XIV., and read again what 

 I said there on this very point, and that without any 

 thought at the time of these statements of Dr Car- 

 penter's. I said, and I again repeat, that if the Cam- 

 bium were an independent structure — that is to say, 

 possessed of inherent powers of growth, and merely 

 dependent on the leaves for supplies of duly elaborated 

 sap, it is impossible to understand why the cutting off 

 in spring of the buds from a particular branch (the 

 adjoining branches of the tree being left entire), should 

 have the effect of preventing the transformation into 

 wood of the Cambium-layer of that branch, — or why 

 the cutting off, in the early part of summer, of all the 

 leaves of another branch (the other branches not being 

 thus mutilated), should have the effect of arresting the 

 further development of the layer. That the facts are 



* Ibidy p. 904. 



