24 BULLETIN 360, U. S. DEPARTMENT OF AGRICULTURE. 



the branches of brooms. These are sometimes so numerous as to 

 cause the branch to resemble a chain of spherical balls. Mistletoe 

 infection on the trunks of spruces in the East often results in the 

 formation of burls; also on the western firs. It can be safely stated 

 that swellings and distortions of the main trunk which persist 

 throughout the life of the tree are a characteristic feature of mistle- 

 toe infection on most conifers of economic importance. 



The spread of the burl tissues tangentially and longitudinally, 

 which, as previously indicated, are frequently inhabited by the 



FIG. 23. Cross section of one of the burls on the Douglas fir shown in figure 22. This 

 section does not pass through the point showing the age at which the infection first 

 occurred. (The tape shows feet in tenths.) 



parasite until a very advanced age, 1 results, as is the case with most 

 species, in cutting off the transporting tissues and hastens the de- 

 cline of the tree (figs. 20, 23, and 24). The bark and wood of the 



1 Meinecke, in 1912 (9, p. 38), records the age of a mistletoe plant (Phoradendron 

 junipcrinum libocedri Engelm.) at approximately 230 years. Species of the genus Razou- 

 mofskya are likewise capable of maintaining themselves to a very advanced age. One 

 instance recorded by the writer may be cited of RazoumofsJcya campylopoda. A cross sec- 

 tion through a mistletoe burl of this species, 3 feet from the ground, on yellow pine a po- 

 sition precluding any but an original infection at an age when the bark was thin showed 

 that the parasite had continuously lived in the burl tissues for 340 years. The old roots, 

 now dead except those immediately next the cambium, could be readily traced to the point 

 of original infection The age of the tree at this point was three years. The burl bore a 

 single fertile aerial branch of the mistletoe. The greater mass of the cortical stroma 

 was entirely without aerial parts, indicating the remarkable condition of parasitism first 

 pointed out by Meinecke for Phoradendron juniperinum libocedri. 



