242 DECAY OF FALLEN LEAVES. [Feb. 



benefit accrues therefrom to the soil or the arboreal vegetation. This 

 is because the mouldering process has become so slow as to have practi- 

 cally ceased. Xo humus is being produced, but the accumulations of 

 leaves are lying dormant, under conditions similarto those of a dry shed. 

 In summer no rain can penetrate to them, and it is in summer chiefly 

 that the rotting process goes on. We may therefore conclude that 

 leaf canopy has a great effect on the formation of humus, and that it, 

 is possible to maintain leaf canopy either on the one hand too close, 

 or, on the other, too open. 



It is possible so to regulate the closeness or openness of the canopy 

 as to delay or accelerate the decomposition of the fallen leaves, and 

 thus to favour the production of humus. The means of effecting this 

 are supplied by the periodical thinnings. It is frequently contrived 

 that these shall be repeated in each part of the forest every ten 

 years ; better still, if they can recur every five years and be more 

 moderate. With a view to the fallen leaves and their importance, 

 the aim of a thinning should be to leave such a degree of canopy 

 that a little light will reach the ground. It should be attempted to 

 leave spaces between the outermost twigs of most contiguous trees, 

 but never to remove a tree which would leave a large space. The 

 spaces or gaps left in the canopy by a thinning should never 

 ordinarily be wider than what may be filled up in a few years by the 

 spread of the crowns and the rapid extension of the side twigs. The 

 degree of canopy aimed at in carrying out a thinning should be such 

 as might permit of the temporary ai3pearance of tufts of grass or 

 weeds here and there, but not for long. In a few years, and con- 

 siderably before the next thinning is due, the spreading of the tree 

 crowns, wherever there was room, ought to have restored completeness 

 to the canopy, and re-established a shade so thorough as to kill the 

 grass. 



The effects of humus and fallen leaves form an intricate subject 

 for investigation, demanding the co-operation of foresters and 

 chemists. A good deal of labour has been expended in this direction 

 Ijy both classes of investigators in Denmark, France, and Germany, 

 and also by individuals combining in some degree both qualifications. 

 Their results, it seems, have sometimes been conflicting, but a sum- 

 mary of them would be desirable before starting, in this country, 

 original investigations. 



X. X. 



