16 



BULLETIN 317, U. S. DEPARTMENT OF AGRICULTURE. 



and are broken off, followed in many cases by a secondary crown 

 (figs. 3, -±, 6, and 7). too late to supply the deficiency in food 

 materials; or the vigor of the present bulk growth and the vitality 

 of the tree are reduced by a general infection throughout the entire 

 crown. The latter type of mistletoe injury frequently occurs. The 

 tree seems to become infected at many different parts of the crown at 

 once, and while the branches are net broken by the formation of large 

 brooms, the vitality of the host gradually sinks under the drain on 

 its resources of so widespread an infection. TThen young trees are 

 infected there is such an excessive broom development by the time 

 they have reached pole size that the original crown has practically 



Fig. li 



A common type of original infection on a larch branch, 

 of branch witches'-brooms. 



showing the beginning 



disappeared. Bushy secondary branches grow out from the stumps 

 of the old ones, and the lopping process may be continued to a third 

 or fourth generation of branches (fig. 2). The width of the second- 

 ary crowns becomes less and less, until practically nothing remains 

 but the stubs of the former branches, bearing a few straggling green 

 twigs (figs. 3. 6. and 7). By this means the assimilatory surface of 

 the tree is gradually reduced. During the period between the fall 

 of the primary and the appearance of the secondary branches, the 

 tree is robbed of a great amount of food material necessary to main- 

 tain its vigor at its present stage, and it begins to show signs of 



