130 FORESTS, WOODS, AND TREES 
On Deeside, according to Mr. Crozier, “the common 
silver fir, formerly one of the most reliable trees, is now 
hopelessly unreliable as a timber crop owing to its 
susceptibility to Chermes. Old trees are immune; but the 
difficulty of raising young stock is likely to lead to its 
extinction altogether as an economic species.” This 
difficulty exists elsewhere, but can be overcome. Young 
plants should be raised under shade in nurseries situated in 
woodlands, and when planted out ought to be always 
mixed with beech. In Wicklow natural seedlings of silver 
fir keep free from Chermes, while planted seedlings close 
by are liable to attack. The attack occurs not long after 
they are planted out, the period when their growth and 
vigour are checked by the act of transplantation. 
Abies grandis.—This is the fastest in growth of all the 
silver firs; and isolated trees in different parts of the 
British Isles often equal and sometimes excel the Douglas 
fir in vigour. Associated with this vigour is good health, 
as, unlike the common silver fir, it is not attacked by 
Chermes, and is not liable to injury from frost in the young 
stage. An acre of this tree in Sussex, which was planted 
in 1900, had attained in 1917 an average height of 35 
feet and a girth of 21 inches. The seedlings are easily 
reared, grow much faster than those of the common silver 
fir, and may be put out when three years old after being 
transplanted once. Abies grandis may be tried as a main- 
crop tree in localities where the common silver fir is 
difficult to establish on account of Chermes and late frosts. 
It is not known whether it will resist wind as well as the 
common silver fir, and it does not bear so much shade as 
the latter. 
The timber in western North America is little known 
commercially; but is probably better than any of the 
other American silver firs except Abies nobilis. It is 
white and soft, yet firm enough to be useful. 
Abies nobilis.—This species is a mountain tree in western 
North America, and differs from Abies grandis in its 
