|Abstract or Summary
- Three species of true firs in the Pacific Northwest--Abies gran-dis, grand fir; A. amabilis, Pacific silver fir; and A. lasiocarpa,
subalpine fir--are severely damaged or killed by an imported insect
pest, the balsam woolly aphid (Chermes (Adelges) piceae Ratz.), Infestations of this insect cause abnormalities in the wood and, in some
cases, result in death of the tree.
Wood samples were collected from five infested and five noninfested
trees of each of the three species. Cross, radial, and tangential sections were taken from the wood samples, and samples were
also macerated to separate the cells. Measurements were made of
four anatomical characteristics: cell wall thickness, cell width, fibril
angle, and tracheid length. Measurements were made of wood that
was produced before infestation of the tree, wood of the same tree
that was produced after infestation, and wood of noninfested trees. Wood produced after infestation in all three species is like compression
wood in that the percentage of summerwood is greatly increased,
tracheids are round in cross section, intercellular spaces
are present, microscopic checking occurs in the cell waIIs, and false
rings are present. The number of rays is almost double the number
found in noninfested trees, and the diameter of the ray cells appears
to be greater. Springwood cell walls of infested trees are sinuous in
nature. Traumatic resin canals in tangential bands may be differentiated
at any time during the growing season.
Cell walls of the springwood of infested trees were significantly
thicker than the springwood ceII walls of wood produced before infestation
and also of noninfested trees for all three species, but there were
no differences with regard to the summerwood.
There were no significant differences in cell width for wood
from each species. This was true for both springwood and summerwood.
Fibril angle in the summerwood and transition area in infested
trees of each species was two to three times greater than the angle
found in wood produced before infestation and in noninfested trees.
No differences in the fibril angle in springwood occurred.
Tracheid length in infested wood was considerably reduced following
infestation. Tracheids of wood produced before infestation,
and in noninfested trees, were approximately one and one-half to two
times longer than tracheids of infested trees.