66 EVERGREENS OF COLORADO 



inhabited by a species of plant louse, belonging to the genus Chermes, 

 which lives upon the juices of the tree and produces the gall-like en- 

 largements at the ends of the twigs. About midsummer the insects have 

 reached maturity, when they pass to the needles of the Douglas fir which 

 may be in the vicinity and upon which they deposit their eggs. This sec- 

 ond generation of the insect passes the remainder of the season upon the 

 Douglas fir. Early in the second summer certain individuals of the insect 

 develop wings and reach the blue spruces, upon which they deposit their 

 eggs. The young lice which hatch from these eggs then attack the needles 

 of the terminal buds and produce a new crop of the abnormal tips. While 



Fig. 52. Front yard over-planted with blue spruce. The owner must 

 prune away the lower branches, or have the view shut off. 



this insect seldom causes much injury to the blue spruce or to the Doug- 

 las fir under forest conditions, it is a rather serious pest upon these trees 

 in parks and upon lawns. It is apt to be most troublesome where the 

 blue spruce and the Douglas fir are growing near together, a condition 

 which favors the insect in its peculiar life history. 



Among the diseases due to parasitic plants are certain malformations 

 known as witches' brooms. These appear as dense, matted growths of 

 twigs upon which the needles are usually somewhat stunted. These 

 witches' brooms sometimes appear in the topmost part or at other times 

 are found hanging against the side of the affected tree. A careful ex- 



