58 THE CONICAL GROWTH OF TREES. 



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 layers is necessarily retained. 



Growth in length and growth in thickness must there- 

 fore 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 enve- 

 loping 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 contempora- 

 neous acts of growth, we shall leave the bark out of con- 

 sideration for the present, and confine ourselves to the 

 wood as the peculiar variable part, and that which princi- 

 pally 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 11, 

 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 visi- 

 ble on the exterior 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 indi- 

 vidual 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 sea- 

 son 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 



