274 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
4. DRAINAGE. 
An elaborate system of drainage, such as is required for the 
growth of agricultural crops, is neither necessary nor practicable 
when dealing with land to be occupied with a crop of trees. For, 
when once established, the trees perform for themselves, in a great 
measure, the necessary drainage. No sooner do they rise to a 
height sufficient to be affected by the wind, than by their own 
movements the soil is loosened around the roots and the superfluous 
moisture readily sinks to a depth at which in most subsoils it 
cannot injuriously affect the health of the trees. By the gradual 
enlargement of the roots also, the soil is more and more broken up, 
and its porosity increased. In planting for ornament alone, the 
ground is generally trenched and drained at a cost equal to what 
is necessary in agricultural practice, but in this case the soil may 
be quite unsuited to the varieties of trees to be planted, without 
such preparation. But, of course, objects other than profit are kept 
in view in such instances. By a proper distribution of the various 
kinds of trees over soils suitable for their respective requirements, 
the expense of draining may be reduced to a minimum. Trees 
which thrive in soils of a dry nature should not of course be 
planted on those of a directly opposite character, and wice versa. 
In general, all that is required is to form surface drains to carry 
off stagnant water. It is very seldom that all the land in large 
enclosures requires draining, but where necessary this should on 
no account be neglected, as no preparation of the soil is of so 
much importance to the health of the trees in the earliest stages 
of their growth. The nature of the soil will determine the 
dimensions of the drains, and the distances at which they should 
be placed apart. If the soil is of a stiff clayey nature, they will 
require to be deeper and closer than in other cases. In general 
it will be sufficient to have the drains cut at from 30 to 40 feet 
apart. The main drains should always be made on the lowest 
part of the ground, and where the easiest natural outfall can be 
obtained. They are usually made 24 inches deep, 30 inches wide 
at the top, and 10 inches at the bottom, and the subdrains 
15 to 18 inches deep. On soils where moorband pan is present 
and in the course of formation, the drains should be made at least 
one year before the ground is planted, in order that the stagnant 
water may get time to drain off, and the soil be made pervious tu 
