MISCELLANEOUS. 



119 



nourished by the descending sap from its leeward 

 branches. 



Indeed, the downward stream of the growth in ^^^^^ 

 girthing may at will be mechanically stopped on one mechani- 

 side of the stem, and projected to the other. This continually 



turned 



may be observed in the natural spiral carved work, from one 



^ ' side of the 



formed by woodbine on the stems of coppice-wood ; f^^^^^^ 

 and doubtless, if instead of the woodbine wu^e were 

 placed spirally up the stems, very regular and beau- 

 tiful patterns might be produced. Wire fences, fixed 

 on the stems of trees, destroy the circulation and kill 

 the sides of the trees on which they are fixed. 



Again, as far as I have remarked, though young 

 1 Dots are round, the older ones greatly incline to the 

 val shape ; and in all the transverse sections of roots 

 ^hich I have examined the eccentricity of the common 

 oint from which the {medullary ?) rays diverge, and 

 ^v^hich is occasioned by the comparatively over-growth 

 of the upper sides of the new annual rings, is very 

 striking. I imagine that this is caused mechanically, 

 and that it is the result of the growth in girthing of 

 the roots meeting with less mechanical resistance from 

 ihe earth on the upper sides. 



As long as a branch root exists, it must, owing to Lateral 



vpward 



its lateral growth in girthing, annually approach the f^^^^^^^^ 

 surface of the ground, and, after that is reached, ascend 

 above the surface. Suppose a root to run horizontally 

 at the depth of one foot below the surface of the earth. 

 Suppose this root to increase only J -in. in diameter 



