134 FORESTS, WOODS, AND TREES 
slender. The Zhuya also greatly improved the soil by its 
thick layer of decaying leaves. Natural seedlings of both 
species were very numerous and vigorous in open spaces. 
Partly blown down and _ partly felled, the plantation 
yielded, 36 years after planting, 7430 cubic feet (quarter- 
girth measurement under bark), or an average annual 
increment of over 200 cubic feet per acre. In wet climates, 
as at Benmore, where the rainfall is over 100 inches, this 
mixture of Douglas fir and Thuya gigantea may be tried 
with success. 
Douglas fir has so far been fairly free from insect or 
fungus attacks, but this immunity may not continue. As 
a precaution, extensive continuous plantations of this tree 
should be avoided; these should be interspersed with belts 
or clumps of beech. Douglas fir is of remarkable utility in 
what may be called interplanting, that is, filling up gaps 
in ordinary woods that happen to be thin and_ poorly 
stocked. It is also invaluable for converting coppice or 
coppice with standards into ordinary high forest, as it usually 
thrives on soils which carry coppice and in a short time 
suppresses by its vigorous growth the coppice shoots. 
Home-grown timber of Douglas fir ranks in quality 
between Scots pine and larch; but it surpasses both in 
dimensions, and is more valuable than either when properly 
grown in dense plantations. It is equally durable with 
larch, the proportion of heartwood at 50 years old being 
about 70 per cent. It converts well, keeping straight when 
long sizes are sawn; and if carefully stacked it dries 
quickly and is not liable to warp. It is somewhat lighter 
in weight than spruce. Home-grown timber has been 
used on the Scone estate for gates, doors, and fencing; and 
was sold for railway sleepers and pit timber. Grown on a 
long rotation, the timber will be found suitable for carpentry 
and joinery. 
Common Spruce.—In addition to the common spruce, 
Picea excelsa, which is a native of continental Europe, there 
are two other species of the genus of value to foresters, 
