MISTLETOE INJURY TO CONIFERS. 



15 



most cases brooms are initiated on the Douglas fir soon after infec- 

 tion. Young seedlings frequently die in the top, owing to the forma- 

 tion of a lateral broom midway on the stem. In the heavily infected 

 regions of Montana, especially in the Clark Fork (Bitterroot and Mis- 

 soula Rivers) drainage, brooming of the Douglas fir is so universal 

 and of such extent that scarcely a single infected tree is free from 

 brooms of some type (figs. 6 and 7). The structure of these brooms 

 is very plainly shown if the tree succumbs to the parasite, as it often 

 does (fig. 7). The formation of brooms invariably results from mis- 

 tletoe infection on 

 the western larch. 

 They may be situ- 

 ated on any part of 

 the branch or at its 

 base (fig. 14). In 

 the latter case the 

 entire branch even- 

 tually dies or is 

 broken off by the 

 wind, and its place is 

 usually taken by a 

 series of short, 

 scrubby secondary 

 branches forming a 

 trunk broom. This 

 broom eventually 

 dies, leaving a large 

 knotty burl of seri- 

 ous consequence not 

 only to the life of the 

 tree but greatly decreasing its value for lumber. Excessive brooming 

 is a common feature wherever infected larch occurs and is the chief 

 cause of injury to the species. In some localities in the Blue Moun- 

 tains of Oregon and parts of Idaho and Montana, where this mistletoe 

 is common, a normally formed larch is seldom found. Instead of the 

 symmetrical, conical crown so characteristic of the normal tree, the 

 crown develops under the influence of the parasite into a denuded 

 spike, bearing only a few ragged branches. When it is recalled that 

 practically every larch in these regions, from pole size up, is more or 

 less infected and seldom attains a normal size, in many cases being 

 killed outright, some notion may be had of the seriousness of the 

 effects of the parasite on its host. 



FIG. 12. Typical broom on yellow pine caused by Razoit- 

 mofskya campylopoda. Note that the end of the branch 

 is dead. 



