LETTER XIV. 



149 



fibres of these roots are regulated as to their amount 

 and distribution by the number, and disposition, and 

 quahty of the plants. 



6. Nor is this all. The crowning argument for the 

 subordination of the Cambium to the buds, and for its 

 absolute dependence on these for its transformation 

 into woody tissue, — and that in a way altogether 

 irrespective of supplies of nourishment, is furnished 

 by one or two very simple experiments, which leave 

 those supplies intact. Cut off in spring, before the 

 process of vegetation is begun, all the buds from 

 one of the branches of a tree ; and at a later period, 

 but in the early part of summer, cut off all the leaves 

 from another branch of the same tree, — leaving how- 

 ever the buds and leaves of the other branches un- 

 injured. In the one case the transformation of the 

 Cambium into wood will he prevented, — in the other, 

 the further transformation of it into wood will be 

 arrested^ — while the buds and leaves of all the other 

 branches being left to grow, the Cambium-layer in 

 every other part of the tree will be duly developed. 

 It is difficult or impossible to understand why this 

 should be, on the supposition that the Cambium- 

 layer is an independent structure, and no farther 

 dependent on the leaves for its development than 

 as these effect the requisite changes in the sap. It 

 is true that the mutilated branches receive no sap 

 from the time they are deprived of their buds or 



