20 



BULLETIN 360, U. S. DEPAETMEXT OF AGEICULTUEE. 



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 jesiv 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- 

 ber of the genus Eazoumofskya effecting an 

 entrance to its host through the mature cor- 

 tex. If apparently recent infections on old 

 parts of trees are carefully examined, the 

 mistletoe ]Dlant will be found to have per- 

 sisted from the time when the branch or 

 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 

 lesults, 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 



Fig. 17. — Area on the main 

 trunk of a yellow pine 

 infected by Razoumojskya 

 campylopoda. The rough, 

 irregular hark indicates the 

 location of the burl tis- 

 sues. A few short mistle- 

 toe plants not visible in 

 the illustration were pres- 

 ent. 



