12 BULLETIN 317, U. S. DEPARTMENT OF AGRICULTURE. 



THE EFFECTS OF MISTLETOE ON ITS HOST. 



A preliminary survey by the strip method made at the foot of a 

 north slope and partly on the level resulted in the accumulation of 

 the data given in Table I. showing conclusively that the larch in this 

 region is heavily infected with mistletoe. Xo attempt was made to 

 ascertain the age of the trees given here, so as to show the degree of 

 suppression. A good idea may be obtained, however, of the nature 

 of the infection, distribution, and quantity of mistletoe present on the 

 trees. In general, the height of the trees here recorded is somewhat 

 less than that of normal or uninfected trees in the same region. 



Fig. 9. — Cross section of the trunk of a larch tree, showing a large burl with white 

 cellulose pits caused by Trametes pini. Note the small amount of living wood and 

 that the dry wood is attacked by fungi and insects. (Tape in feet graduated in 

 tenths.) 



The youngest specimen found infected was less than 5 years old, 

 which means, of course, that such early infection will not allow a 

 very high state of merchantability to be attained, even if the young 

 tree is not killed prematurely. Usually very young growth first be- 

 comes infected somewhere on the trunk where the bark is not yet 

 protected by cork (fig. 11). The infection of very young seedlings 

 causes them to assume various abnormal shapes and positions, espe- 

 ciallv when the mistletoe is confined to one side of the stem. Burl 



