LETTER XVI. 



173 



died off as the tree grew upwards, the Cambium-layer 

 is duly transformed into wood eyen at its lower part, 

 although this may be very remote " from the leaves 

 above. In this case, however, the Cambium is in the 

 direct line of the leaves, i, e. (according to my theory) 

 of the plants above, and, being the roots of these, is 

 of course developed. And it may serve to give force 

 to this consideration if I observe, in regard to the case 

 of the mutilated branches, that were the terminal buds 

 merely, or the terminal leaves merely, to be left 

 uninjured (all the others being stript off), the Cam- 

 bium-layer would in hke manner be developed through- 

 out. Nor is this all. The extent to which this layer 

 is developed in the case both of the fir and the branches 

 will be proportioned to the amount of the leaves ; and 

 the woody layer will be thin because these are/6^^/, — 

 contrasting strongly with the much greater thick- 

 ness it attains in the other branches and in other 

 firs similarly circumstanced, but provided with side- 

 branches and laden' with foliao-e. 



10. Add to all this, what I dwelt so much upon in 

 Letter XIV., and which it would be tedious here to 

 repeat, regarding the varying thickness of this layer 

 as transformed into wood, on different sides, according 

 to the position on the tree of the several buds and 

 plants, — and likewise the facts and considerations 

 relative to the winding conrse of the hgneous fibres in 

 most if not in all trees, — and their otherwise singular 



