146 



LETTERS ON TREES. 



omitted one consideration, not inferior in importance 

 to anj of those then adduced. 



3. It is this : That the Cambium is wholly subor- 

 dinate to the buds, and its development into woody 

 tissue entirely dependent on the plants that issue from 

 the buds — while, further, the degree or extent to which 

 it is developed is very exactly proportioned to the 

 number of the plants, the vigour of their growth, and 

 their position on the tree. It is true that the Cam- 

 bium cannot grow without supplies of duly elabo- 

 rated" sap, and that the leaves are the organs in which 

 tliis elaboration is effected. But were the layer in 

 question otherivise independent of the leaves, it ought 

 to grow uniformly all round the tree, without refer- 

 ence to the number, or the position, or the vigour of 

 the plants above. Its own inherent powers of growth 

 would be equably exerted on every side, while the 



attractive" force thence resulting would ensure for 

 it not merely an adequate supply, but a uniform dis- 

 tribution of the nutritive materials prepared in the 

 leaves. There is nothing: that I know of in the struc- 

 ture of that layer, and there ought in this view to be 

 nothing in its connection with the leaves, to hinder the 

 freest access of the descending sap to every part where 

 supplies are needed. 



4. But what do we find on examining the concen- 

 tric woody circles ? Look again at the adjoining 

 figures, to which I formerly directed your attention, 



