58 THE CONICAL GROWTH OF TREES. 



The conical growth of the tree is the result of the conical for- 

 mation of the first year's shoot, which is the foundation of the 

 subsequent annual additions of wood and bark ; for as these are 

 deposited in strata, which lie parallel with the wood and bark 

 of the first year's shoot, the conical form of the superposed lay- 

 ers is necessarily retained. 



Growth in length and growth in thickness must therefore be 

 hereafter regarded, not as two different factors, but as the result 

 of one and the same vegetative cause, viz., the formation each 

 year of a new conical layer or enveloping mantle of wood and 

 bark, which extends from the top to the bottom of the tree. In 

 order to make clear the connection which subsists between these 

 two cotemporaneous acts of growth, we shall leave the bark 

 out of consideration for the present, and confine ourselves to the 

 wood as the peculiar variable part, and that which principally 

 determines the thickening of the entire axis. 



The annexed figure represents an ideal longitudinal view of 

 the primary and secondary axes of the Beech branch already 

 prefigured and described in Chapter II., and is intended to 

 illustrate the nature of conical growths, and the connection 

 which subsists between the axis and its ramifications. 



It is quite plain that, as each new cone developes from the 

 terminal bud which is situated at the summit of the previous 

 year's cone, the sets of bud-rings which are visible on the exte- 

 rior bark of the young stems and branches of trees, and which 

 mark the growth of each year, must correspond respectively 

 with the summits of each individual of the superposed series of 

 cones; and that, as these cones are formed by the leaves of each 

 year, their summits rise above one another according to the 

 greater or less amount of vital activity of the leaves during the 

 season of growth. Hence, figures '53 point out the summit of 

 the first and innermost cone, which corresponds exactly with the 

 position on the exterior bark of the first set of bud-rings. It is 

 the same with the tops of the other enveloping cones marked '54, 

 '55, '56, and '57. The figures indicate not only the tops of the 

 cones, but, at the same time, the place of the annular scars left 

 by the bud-scales on the bark. 



Hence, in order to estimate the age of an axis from a given 



