50 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
as subordinate species on suitable land. These are valuable 
timber-trees, which deserve a trial, and many often prove profitable 
additions to the crop. 
Maintenance for Twenty-five Years.—¥or several years after 
planting, the plants may require to be kept free from weeds 
of all sorts, and failures will have to be replaced. For this latter 
purpose, where the situation is at all suitable, perhaps nothing 
will succeed better than Douglas fir and sycamore, which are 
of rapid growth, and can stand side-shade. The fencing should 
also be frequently inspected, to prevent damage by stock or 
game. All open drains or water-courses should be seen to, so 
that no obstruction interferes with the free motion of water. 
Damage by ground-game should be carefully looked for, and 
exterminative measures promptly taken in hand. All plants, 
especially the hardwoods, should be looked after for a number 
of years, and double-leaders and disproportionate branches cut 
back. Double-leaders in conifers, when within reach, may be 
checked by nipping out the side-buds. 
Thinning constitutes the next operation. If the plantation has 
been judiciously formed and well attended to hitherto, the manner 
in which thinning is performed will greatly influence the future 
value of the produce. There is no definite age when thinning 
should become necessary, nor can any distance be laid down 
as that at which the trees should stand apart. This depends on 
the increase in height, and the individual growing-space required 
by each kind of tree, while soil, altitude, and exposure also 
occasion inequalities in the growth, and exert their own special 
influence affecting thinning. 
A certain proportion of healthy foliage is at all stages of 
growth necessary for the production of a sound and valuable 
crop of timber. But, on the other hand, if the trees stand too. 
wide apart, or thinning be commenced too early, thus allowing 
the branches of each tree to become strong and spreading, the 
timber produced will be coarse and open in the grain, and 
full of large knots or even black holes. In thinning, the principal 
object ought always to be to assist nature to produce the best. 
class of tall, clean, and well-formed timber, with few branches, 
by keeping the trees close enough to check the growth of 
unnecessary side-branches. The lower branches will then grad- 
ually die and fall off, and when the mature timber is cut up, 
it will be found to be clean and close-grained. 
