148 



LETTERS ON TREES. 



5. Take a tree, for example, from the middle of a 

 plantation of Firs, thickly set together — in which part 

 the trees grow only at the top, and rise up as bare, 

 narrow poles — and compare its woody cylinders with 

 those of another tree taken from the outskirts of the 

 plantation, where the side plants of the trees as well 

 as the vertical have had full scope. Compare, again, 

 the circles in a tree taken from the south side of such 

 a plantation with those in a tree taken from the north 

 side. Carry the comparison a step farther, and note 

 the differences between the circles in any one or all 

 of these trees and those of a Fir of the same species 

 that has grown by itself in an open but well sheltered 

 park, where it has had room to grow freely, and to 

 spread in all directions. If the Cambium-layer be 

 essentially an independent structure, and possessed of 

 innate powers of growth, whence the differences, which 

 you cannot fail to perceive, in the thickness of the 

 woody layers, and whence the uniformity in the rela- 

 tion which they bear in that respect to the amount 

 and to the character of the vegetation going on above? 

 The legitimate inference from the facts, and the pro- 

 per answer to the questions, is, that the Cambium-layer 

 is not an independent tissue, but one subordinate to 

 the buds, and that it is ill or well developed, equally 

 all round or partially here and there, and differently 

 in different years, just because it is virtually the roots 

 of the plants that come of the buds, and because the- 



