22 



BULLETIN 360, U. S. DEPARTMENT OF AGRICULTURE. 



oils, large barrel-shaped swellings, from which pitch usually exudes 

 in large quantities. Infection on one side of the tree generally re- 

 sults in the type of burl shown in 

 figure 19. 



Burl formations resulting from 

 mistletoe are a common feature 





FIG. 19. Common type of burl on yellow 

 pine caused by RazoumofsJcya campylo- 

 poila. The tree is 3 feet in diameter at 

 this point. 



on western hemlock wherever the 

 parasite occurs in quantity. The 

 same is true for the mountain 

 hemlock. In the Marble Creek 

 region of the St. Joe National 

 Forest mistletoe burls on the 

 hemlock are of frequent occur- 

 rence. Allen (1, p. 20-21) writes 

 of this type of injury as follows: 

 " If, however, the plant gets 

 foothold on the leading shoot, a 

 burl follows which persists 

 throughout the life of the tree 

 and not only ruins a log, but ren- 

 ders the tree apt to be broken by 

 the wind." Infection on the main 

 trunk of lodgepole pine is often 

 attended by long fusiform swell- 



ingS as the parasite . progresses 

 from the Original point of in- 

 fection. This may Continue Until 



the bark becomes so hard that the plants can not push up through 

 it and the spread of the parasite ceases (fig. 20). The parts 



tn e spread of the parasite from the original 



^erffrfquenUy'dL, ^avin^an^pen wound* 

 (Photographed by George G. Hedgcock.) 



