MISTLETOE INJURY TO CONIFERS. Ze 
infected, however, may continue to produce aerial branches of the 
mistletoe to a very advanced age. True mistletoe burls are probably 
of less frequent occurrence on Douglas fir than on any other economic 
tree species. Burls do occur, however, with sufficient frequency to be 
characteristic of mistletoe infection on the trunk of this tree. Large 
elongated mistletoe burls, including the entire circumference of the 
trunk, occasionally occur in heavily infected trees in many parts 
of Idaho and Montana (fig. 21). More frequently there is a series 
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Fic. 21.—Large mistletoe burl on Douglas fir F!G.22.—A Douglas fir, showing numer- 
caused by Razoumofskya douglasii. This ous burls caused by Razoumofskya 
burl is approximately 10 feet long and 2 douglasii. The branches are heavily 
feet in diameter at its widest part. broomed. A high degree of infection, 
but a common condition, is shown. 
of individual burls, more or less confluent, on one trunk (fig. 22), 
each burl representing the seat of an old infection, from which the 
aerial parts of the parasite have long since disappeared. Longitu- 
dinal and cross sections through these burls show the characteristic 
fan-shaped areas of infection (fig. 23). In numerous cases the burls 
originate from infections at the base of branches. If the branch 
dies or is broken off, an open wound is formed in the center of the 
burl. Very peculiar swellings or small burls frequently occur on 
