BULLETIN" 317, I*. S. DEPARTMENT OF AGRICULTURE. 



common to find them lopped off by the wind. This is especially true 

 of tall stems that have come up in close canopy and afterwards 

 become more or less isolated. In the case of the larch the ill effects 

 of the wind are greatly augmented by the heavy loads of long, trail- 

 ing lichens (Alectoria fremontii Tuck, and TJsnea longissima Ach.) 

 supported by the branches (fig. 3). During rainy periods these 

 lichens, through the absorption of large quantities of water, increase 

 the weight of the branch by several pounds and, hanging downward 

 in a saturated condition, offer a greater resistance to the wind. The 



amount of damage to the 

 larch in many locations 

 from this cause alone is 

 much greater than is ordi- 

 narily supposed. In the 

 study in the Whitman 

 National Forest it devel- 

 oped that the injury to the 

 larch by mistletoe (aside 

 from the gradual effects of 

 suppression by brooming 

 up the branches and reduc- 

 ing the assimilatory sur- 

 face) was in a large meas- 

 ure due to the pruning by 

 the wind of the many 

 branches w h i c*h , being 

 heavily loaded with 

 witches'-brooms, caused an 

 increased weight to be ex- 

 erted at their bases. These 

 brooms are often formed 

 far out on the branch and 

 become densely matted with 

 dead leaves and lichens (fig. 3). This increase in weight often 

 amounts to several pounds more than that of a normal branch of the 

 same age and size (Table II) and is further increased by the absorp- 

 tion of water during rainy weather. In the winter the broom fur- 

 nishes a collecting place for snow. It is very evident how the re- 

 sultant of the two forces, viz, the wind in a lateral and the weight 

 of the broom-laden branch in a vertical direction, may bring about 

 the removal of all the main original branches (fig. 4). It is not 

 uncommon to find large heaps of branches heavily loaded with 

 brooms under the infected tree. Up to this point the breakage of 

 normal wood uninfected bv mistletoe roots has alone been considered. 



L'icj. 4. — A larch, showing the original crown entirely 

 removed by brooming. The secondary crown is also 

 broomed. The witches'-brooms support large quan- 

 tities of "black moss" {Alectoria fremontii Tuck.), 

 which grows over and mats the foliar spurs. 



