COMMON, OR NORWAY SPRUCE FIR. 465 



we have already observed, should be planted in thick 

 masses by itself, or mixed with other trees ; but where 

 ornament is the object, and the full developement of its 

 form is desired, it must, from the earliest age, be kept 

 free from the contact of any other tree, and allowed scope 

 for the full growth and elongation of its lateral branches, 

 which, under such circumstances, become persistent during 

 life, and upon whose retention the beauty and perfect 

 cone-like form of the tree depends. 



It seems subject to few diseases, but, from the resistance 

 its thick close foliage and unyielding spray offer to the 

 wind, is liable, upon light soils super-imposed upon a 

 harder substratum, to be blown up by the roots, or even, 

 in sudden gusts or hurricane-like storms, to have the trunk 

 snapt right asunder at a less or greater distance from the 

 root. The only insect which affects its health and growth 

 in Britain is a species of aphis, whose attacks, however, 

 seem almost confined to young trees under fifteen or 

 twenty years old, but which, though injurious, we have 

 never observed to prove fatal to the tree. The effect 

 produced is easily observable in the 

 pseudo cone-like excrescences which 

 are so frequently seen upon the side 

 shoots of young Spruce Firs, and which 

 seem to originate in the following man- 

 ner : in the autumn the parent aphis 

 deposits her eggs at the base of the 

 embryo leaves within the buds destined 

 to produce the shoots of the following 

 year ; when these begin to burst and 

 expand in spring, the leaves at whose bases the eggs 

 have been deposited, instead of increasing in length, en- 

 large at the base and form a cell or cyst, whose mouth, 



2 H 



