MISTLETOE INJURY TO CONIFERS. 35 



young infections on nursery stock to escape detection. Accordingly, 

 young infected seedlings may become a means of distributing and 

 establishing the parasite in plantations generally, not only locally 

 but to far distant regions, when growing stock is shipped either for 

 experimental purposes or for permanent plantings. That this is 

 possible is shown by the discovery in the planting areas near Wal- 

 lace, Idaho (Coeur d'Alene National Forest), of a yellow-pine 

 seedling showing a very recent infection of mistletoe. Since the 

 plantings were made on a widely denuded area and no yellow-pine 

 mistletoe is as yet known to occur in the immediate region, it seems 

 that the seedling must have become infected while at the home 

 nursery at Boulder, Mont., where this mistletoe occurs. In view of 

 the fact that there is a very grave danger of transporting agents 

 injurious to forest growth, either fungous diseases or mistletoe, by 

 sending nursery stock to distant parts of the country, the need of 

 strict sanitation in the neighborhood of forest-tree nurseries can not 

 be overemphasized. Whenever new nursery sites are planned in or 

 near forests, a close pathological survey should be made of the 

 surroundings, and trees diseased or suppressed from any cause what- 

 ever should be cut out. This should be done also where nurseries 

 are already established. 



The influence of the physical type on the severity of attack should 

 receive considerable attention in any plan of management of forests 

 in mistletoe regions. Forest Assistant Gilkey. in a report on the 

 western larch of the Whitman National Forest, states that " a total 

 of several hundred trees in various parts of the forest shows 79 per 

 cent of the larch to be attacked on the dry-slope type, with only 27 

 per cent on the more moist sites." The writer's own investigation in 

 the same forest shows an even greater difference between the moist- 

 valley type and the more exposed slopes, which was 87 per cent for 

 the latter and 15 per cent for the former. The severity of the infec- 

 tion on yellow pine and Douglas fir in other regions likewise shows 

 wide extremes as influenced by elevation and exposure. Mr. E. E. 

 Hubert, of the Laboratory of Forest Pathology, reports from ex- 

 tensive observations during a reconnoissance of the lodgepole pine 

 in the Big Hole Valley, Mont., that the most favorable sites for 

 mistletoe are exposed dry ridges and south slopes, where the infec- 

 tion ranges from 50 to 70 per cent of the stand. In the valley type 

 the percentage of infection was much lower. 



In view of the fact that all economic species so far observed are 

 subject to attack at any age, it is hardly possible to establish an age 

 at which infection becomes so serious as to interfere with the mer- 

 chantability of the host. In regions of heavy mistletoe infection it 

 would be quite impossible, for the reason that there is a much greater 

 chance for all age classes to become infected. In numerous in- 



