56 FOREST TREE DISEASES. 



it grows on. The irritation of the cambium by the 

 roots of the mistletoe results in a considerable swelling 

 of the branch at the point of attack. The wood of such 

 swellings is very characteristically marked by longitu- 

 dinal rows of small holes made by the sinkers. The 

 holes caused by the sinkers of Phoradendron are par- 

 ticularly conspicuous. 



Mistletoes do not often kill outright. Girdling by 

 Razoumofskya can even stimulate for quite a time the 

 growth of the branches and leaves above the point of 

 attack. This luxuriant growth, however, is of little 

 benefit to the tree. The food prepared in the excess 

 foliage above the mistletoe serves to nourish the mistle- 

 toe plant, and barely sufficient food is allowed to go 

 below to the roots to keep them from starving. In 

 many cases the attack ends in the death of the branch 

 or limb, and when many limbs are affected in the death 

 of the tree. Razoumofskya very often causes a forma- 

 tion of witches' brooms (p. 21). Large formations of 

 this kind, often resembling richly branched, low- 

 hanging limbs, with profuse foliage, are very conspicu- 

 ous on sugar pine, yellow pine (PI. XXII J), and Jef- 

 frey pine, and common on lodgepole pine (PI. XXIV) 

 and Douglas fir. Phoradendron sometimes lives for 

 a great many years and then causes swellings and 

 deformations, for instance, on trunks of incense cedar, 

 where the -parasite has been known to live for more 

 than 220 years. As the rather brittle mistletoe shrubs 

 break off easily, rarely lasting more than 10 years, 

 new shrubs are formed from buds breaking through 

 the bark of the host, as long as the bark is not too 



