20 BULLETIN 360, U. S. DEPARTMENT OF AGRICULTURE. 
extra food materials in the healing tissues at this point exercised a 
beneficial influence on the parasite. 
The actual nutritive relation between these parasites and their 
hosts is not at present well understood. The constant removal of 
all the needles of six lodgepole pines 8 to 12 years old on which 
large clumps of mistletoe were attached has not in the second year of 
the experiment resulted in the death of either the host or parasite. 
The controls, viz, six young pines of the same age, stripped of their 
needles but bearing no mistletoe plants, have died. This experi- 
ment indicates a possible transfer between the host and parasite not 
only of water and inorganic salts, but of or- 
ganic food materials as well. However it 
may be interpreted, it seems that the pines 
were kept alive temporarily by the mistletoe. 
Probably it is a mutual subsistence on stored 
materials. It must be remembered that the 
whole tendency of the activities of these mis- 
tletoes (Razoumofskya spp.) is to reduce the 
life functions of the host to their lowest 
point, and this is the fact that should be of 
chief concern to the forester. 
RESULT OF INFECTION ON THE TRUNK. 
Another form of mistletoe injury results 
when infections occur during the early life 
of the tree, with the formation of burls on 
+ the trunk. No case is on record of any mem- 
ee ee ee ae ber of the genus Razoumofskya effecting an 
infected by Razoumofskya entrance to its host through the mature cor- 
eae ane oust tex. If apparently recent infections on old 
location of the burl tis: parts of trees are carefully examined, the 
si ES few short mistle’ mistletoe plant will be found to have per- 
plants not visible in : 
the illustration were pres- sisted from the time when the branch or 
eee trunk was young. Until it is proved by 
actual inoculation that the parasite is able to penetrate the mature 
cortex with its outside covering, commonly called the bark, the fore- 
going statements must remain valid. 
Burls on the trunk caused by mistletoe are very common for 
some hosts, but vary in frequency on others. In point of frequency 
the western larch is most, seriously affected by this kind of injury. 
Two types of burls occur on this tree, determined by the nature of 
the original infection. If the infection occurs at the base of a 
branch (fig. 11) and travels to the main trunk, a basal branch burl 
results, giving rise to a broom, which later dies, leaving a great burl, 
often of large proportions. If infection occurs directly on the main 
trunk the beginning of a trunk burl! is immediately initiated. With 
