MISTLETOE INJUEY TO CONIFERS, 



11 



able trees. Considering the severity of the infection, they could 

 not be expected to attain near the size of their parents shown in 

 Plate III, figure 1, and from which they received the mistletoe. 

 Of the 245 infected seedlings, 49 were dead. An examination 

 of the root system of each 

 seedling showed it to be well 

 developed. In the absence 

 of any other deteriorating 

 influence except an occa- 

 sional needle infested by 

 Chionaspis pinifolia Fitch, 

 the death of these seedlings 

 must be ascribed to the lux- 

 uriant growth of mistletoe 

 which they had supported 

 (fig. 5). In most cases the 

 tufts of mistletoe had fallen 

 away. The bark of the 

 large fusiform swellings 

 was usually ruptured and 

 both the wood and bast tis- 

 sues were so heavily infil- 

 trated with pitch that the 

 passage of food materials 

 between the crowm and the 

 roots was wholly impossible, 

 resulting in death. In this 

 respect there is a parallel 

 between this type of mistle- 

 toe injury to seedlings and 

 that resulting from the 

 perennial mycelium of some 

 caulicolus Peridermiums. 



A further study of the large trees shown in Plate III, figure 1, is 

 illuminating. Two of them, the right and the left in the figure, are 

 dead. . Scarcely a single normal branch is to be seen, but instead are 

 numerous large gnarled and distorted brooms. These trees measured 

 on an average 9.3 inches in diameter at 4^ feet from the ground, and 

 increment borings showed the age of each to be 190 years. This is 

 far below the diameter of normal trees of the same age for the 

 region. A careful search for secondary causes of injury resulted 

 negatively. The trees were absolutely sound. Lightning injury, 

 which sometimes causes spiketop in yellow pine and other conifers 

 and which sometimes is erroneously attributed to mistletoe, was not 

 present. With the evidence in hand, it is safe to state that the trees 



Fig. 8. — A group of Douglas firs with their entire 

 lower crowns developed into brooms by Razou- 

 mofski/a douglasii. Note the sparse foliage of 

 the upper crowns and the young brooms in the 

 tree on the right, showing how the parasite 

 travels upward. The branches between the 

 brooms have died from lack of nourishment. 



