CHAP, xi.] Effects of Underplanting 243 



assimilative functions would naturally be induced, which would 

 certainly lead to the production of a larger quantity of timber 

 but of lower specific gravity, and consequently of less technical 

 utility, than was being formed previous to the artificial inter- 

 ruption of the leaf-canopy. 



And, at the same time, the underwood, as it gradually grows 

 up into the lower portion of the crowns, is of practical utility in 

 cleaning the boles by interfering with the vital functions of the 

 lower branches, and suppressing the activity of their foliage. 

 It thereby also helps to concentrate and confine the constructive 

 functions within the upper regions of the bole chiefly, so as to 

 increase the girth of the top-end relatively to that of the base, 

 and thereby enhance the technical and financial value of the 

 stem. These advantages must of course be counterbalanced 

 if the underwood be allowed to grow up so far as to interfere 

 with the normal development of the standards or to cause 

 partial suppression of the crowns. 



The quantitative relation of the heartwood to the sapwood in 

 tree-growth is still an unread chapter in the great book of the 

 laws of nature. Up to the present, practically nothing is known 

 about this matter. Riinnebaum and others have shown that in 

 Pine woods underplanted with Beech the proportion of heart- 

 wood to sapwood is greater than in Pine standards growing 

 without underwood ; but as similar benefits can be proved in 

 the case of mixed woods of Pine, Spruce, Beech, &c., there is 

 as yet no sound basis for justifying the assumption that 

 underplanting specially favours any shortening of the period 

 of semi- activity which the older sapwood has to pass through 

 before attaining its full maturity as the kern or heartwood of 

 the tree. 



Undoubtedly the greatest influences exerted by undergrowth 

 are to be found, firstly, in the richer stores of humus or leaf- 

 mould with which it provides and enriches the soil through 

 the decomposition of its annual fall of leaves and twigs, whereby 

 all the physical properties of ordinary woodland soils become 



R 2 



