120 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
apart, the nurses only being removed in the case of hardwoods. 
No doubt this method provides for the welfare of individual trees 
better than any other; but sylviculture recognises the claims of a 
mass or number of trees collectively, rather than the special 
requirements of the units which compose the mass, and aims at 
growing timber and not merely ¢rees, and therefore we might 
consider whether the usual method of thinning is the best to 
attain the object in view. In all natural forests it is evident 
that the operation of thinning by means of the axe and saw 
has never been carried out, and yet it is from such forests that 
our best timber supplies have been drawn, and an endeavour 
will be made to show the reason of this fact. Let us take the 
case of a piece of heath-covered ground that is being self-sown by 
Scots fir. Here we find the plants that show themselves first 
scattered here and there over the ground, some of them separated 
from each other by 20 or 30 feet. Every successive year a few 
additional plants appear, gradually filling up the blank spaces, until 
the whole surface of the ground is eventually covered with plants. 
By this time, however, the first plants that appeared will be con- 
siderably in advance of their youngest neighbours, and will have 
acquired a certain amount of superiority over the others, according to 
their age and vigour. It is evident that if nothing occurs to stop 
the growth of these larger plants, they will be in no danger of being 
overtopped or smothered by thei neighbours, but will continue 
growing until they have reached their full height. But although 
they may have free space for upward growth, they may be checked 
or stopped altogether from developing their lateral branches by 
smaller but equally vigorous plants that are growing up around 
them. Suppose a large plant to be 6 or 8 feet in height at the 
time a smaller plant, standing 6 feet away, is only 3. Assuming 
the lowest branch on the former tree to extend 3 feet in the 
direction of the latter, it would allow a space of nearly 3 feet 
between the nearest branches of the two trees, assuming the branch 
in question to be the longest on the side of the tree. This space 
would gradually decrease until the branches of the two trees 
touched, when their growths would be checked and ultimately 
stopped, causing their death. Other branches, higher up on the 
stems of the two plants, would, however, be meeting in the same 
way and sharing the same fate, always leaving, however, a clear 
space between the leading shoot of the smaller plant and the nearest 
branch opposite on the larger. Supposing the two plants to keep 
