THE SHAPES OF BRANCHES. 147 



shoot ; I a lateral branch near the top, and c a lateral branch 

 lower down. There is here a double exemplification. While 

 the branch a, as a whole, has its branchlets arranged witb 

 tolerable regularity all round, in correspondence with its. 

 equal exposure on all sides, each branchlet shows by its; 

 curve as much bilateral symmetry as its simple form permits. 

 The branch 6, dissimilarly circumstanced on the side next 

 the main stem and on the side away from it, has an approxi 

 mate bilateralness as a whole, while the bilateralness of its 

 branchlets varies with their respective positions. And in the 

 branch c, having its parts still more differently conditioned, 

 these traits of structure are still more marked. Extremely 

 strong contrasts of this kind occur in trees having very 

 regular modes of growth. The uppermost branches of a 

 Spruce-fir have radially-arranged branchlets: each of them,, 

 if growing vigorously, repeats the type of the leading shoot, 

 as shown in Fig. 203, a, b. But if we examine branches 

 lower and lower down the tree, we find the vertically-growing 

 branchlets bear a less and less ratio to the horizontally- 

 growing ones; until, towards the bottom, the radial arrange 

 ment has wholly merged into the bilateral. Shaded and 

 confined by the branches above them, these eldest branches 

 develop their offshoots in those directions where there is 

 most space and light: becoming finally quite flattened and 

 fan-shaped, as shown at Fig. 203, c. And on remembering- 

 that each of these eldest branches, when first it diverged 

 from the main stem, was radial, we see not only that between 

 the upper and lower branches does this contrast in structure 

 hold, but also that each branch is transformed from the 

 radial to the bilateral by the progressive change in its en 

 vironment. Other forces besides those which aid or 

 hinder growth, conspire to produce this two-sided character 

 in lateral branches. The annexed Fig. 204, sketched from 

 an example of the Pinus Coulterii at Kew, shows very clearly 

 how, by mere gravitation, the once radially-arranged branch- 

 lets may be so bent as to produce in the branch as a whole a 



