60 THE CONICAL GROWTH OF TREES. 



point taken below the terminal bud ; it is only necessary to 

 count the number of sets of bud-rings on the exterior bark, or 

 of years' rings visible in the wood on the cross section of the axis, 

 as both numbers will be found to correspond invariably with 

 each other. To make this plain to the reader, the diagram 

 shows not only the relative position and number of the several 

 conical growths, but their respective lengths and breadths at the 

 same time, the latter being visible at the bottom of the diagram 

 in the form of a corresponding number of circular and concen- 

 tric woody layers or strata. 



The following simple geometrical consideration will, we hope, 

 aid the reader in obtaining an approach to a proper conception 

 of the relation subsisting between growth in length and increase 

 in breadth among the branches of trees. If he regards the dia- 

 gram attentively for a few moments, he will see that the two 

 sides of the innermost cone, estimated from the point immedi- 

 ately below the terminal bud marked '53, form, with the diameter 

 or breadth of the cone at its base, an isosceles triangle. Now, 

 supposing the base of this triangle to remain constant and its two 

 sides to vary, it is plain that the angle of acumination formed 

 at the apex of the triangle will be a function of its sides, for 

 this angle will become greater or smaller, in proportion as we 

 suppose the apex of the triangle to approach to or recede from 

 its base, and its two sides to shorten or elongate. For the shorter 

 and more abbreviated the axis of the cone, the more relatively 

 enlarged is its base, and the more clearly is it conical ; but the 

 more its axis is lengthened, so much the more do the two sides 

 of the cone approach to a state of parallelism, and the axis tend 

 to a cylindrical form. 



These considerations prove that the following law will express 

 the relation subsisting between the two dimensions of length and 

 breadth; the branches are more cylindrical the longer they are, 

 and more conical in proportion as they are shorter. 



As examples of well-marked conical growth we may mention 

 those extremely abbreviated, or, more properly speaking, abortive 

 shoots, called thorns, of which (Cratcegus crus-galli) the Cock- 

 spur thorn furnishes us with an admirable instance. In the case 

 of (Salix Babylonicd)\hQ Weeping Willow, on the contrary, we 



