APPLICATION OF THE METHOD. 87 



and should in consequence be repeated more fre- 

 quently. 



They may be commenced then after the crop has 

 reached the sapling stage, and the denser the seed- 

 ling-crop is at the beginning, the sooner will it become 

 necessary to undertake this operation. When the 

 forest has grown up into low poles the stock must 

 be opened out still further, and a severe thinning 

 must be made when the bole has almost attained its 

 full height. Although one of the conifers, a group 

 of trees whose wood gains in quality by slow growth,* 

 the Scotch pine requires these heavy thinnings, for 

 they alone will enable it to form an ample crown, 

 and thus allow its tissue to become better lignified. 

 In all these thinnings, it is obvious that as far as 

 possible those trees should be removed which are 

 deformed from some cause or another, or which ex- 

 hibit black spots on the upper part of the bole, a sure 

 indication of an unhealthy accumulation of resin 

 in the woody tissue, and hence of approaching decay. 



* This is just the reverse of what occurs among those broad-leaved 

 species alluded to above (vide note p. 52) in which the larger and 

 more numerous vessels are grouped together in the " spring-wood." 

 Vessels are entirely absent in the wood of conifers, which is com- 

 posed of a peculiar kind of tissue (pitted areolar tissue) and short 

 fine medullary rays, and also, in some species of resin-ducts. The 

 wood-cells in the exterior of each annual ring, i.e., in the " autumn 

 wood," are much smaller, thicker-walled and better lignified, than 

 those of the inner portion or " spring- wood." Moreover, here it is 

 the latter that increases with rapidity of growth, the width of the 

 autumn wood being almost constant. A fast grown conifer will 

 therefore show a larger proportion of spring-wood than a slow grown 

 tree under the same conditions of vegetation, while the amount of 

 the autumn wood will be about the same in each. Hence for all 

 conifers the slower the growth, the denser will be the wood. 



