GROWTH OP TREES. 149 



II. That the successive formation of the layers of 

 wood is produced by the evolving of buds. 



III. That the annual formation of woody layers is 

 owing to the pulp, which, every year, forms at one and 

 the same time, a new layer of pulp wood, and a new 

 layer of inner bark. 



Our oaks and elms seldom exceed thirty feet in 

 circumference ; but the great chestnut tree on Mount 

 JStna is reported to be one hundred and sixty feet in 

 circumference. 



Growth in height, again, arises from the impulse 

 given to the sap in spring, which rises first in the hard 

 wood ; and, as the season advances, in the sap-wood of 

 the previous year. This expands the buds, and from 

 the upper part of the stem young shoots rise, which, 

 of course, possess one layer less than those of the pre- 

 ceding year ; and by thus going down to the root in a 

 tree ten years old, for example, we find ten rings at 

 the base, while there are only nine above the second 

 shoot, and only one at the summit. 



Our forest trees seldom exceed one hundred feet in 

 height, and are rarely so high as this, while palms 

 often reach one hundred and fifty feet, without in- 

 creasing an inch in thickness from the root to the 

 summit. Von Martius describes one fifteen feet high, 

 and not thicker than a man's thumb. The flower- 

 stalk of the American aloe often reaches thirty feet, 

 and M. A. Richard has seen this in another species 1 



(J) In Latin, Agave faetida. 



