34 BULLETIN" 360^ U. S. DEPARTMENT OF AGRICULTURE. 



of mistletoes (PL IV, fig. 2) . In this class would fall the firs, spruces, 

 arbor vitres, cedars, junipers, and yews. If this can not be clone, 

 owing to certain requirements by these species on soil and climate, the 

 stand should be composed of as many different species as possible. 



Aside from reasons already set forth, isolated seed trees heavily 

 or even slightly infected by mistletoe should not be retained. The 

 vigor of the parasite on the parent tree will become greater, owing 

 to its response to open and well-lighted conditions. Reproduction 

 under the tree and in its near vicinity, if of the same species, will 

 readily become infected. The same will be true of seed plats. The 

 force developed within the mature seed capsule of these mistletoes 

 and exerted in the expulsion of the seed is a factor of great signifi- 

 cance for the spread of the parasite. It has been demonstrated in 

 the case of one species that this force is sufficient, starting at an 

 elevation of 8 feet on the level, to carry the seed a distance of over 

 66 feet. In addition to the forcible expulsion of its seeds by the 

 parasite, strong wind is an important factor in seed dissemination. 

 In one instance seeds of the larch mistletoe were collected in number 

 from the roof of a cabin one-fourth of a mile aAvay from the nearest 

 infected tree. This is not at all extraordinary, in view of the fact 

 that the larches of the region are very tall and are heavily infected 

 in the crown. Also strong winds are frequent during the period of 

 seed maturity. Birds and animals play a minor role in the distri- 

 bution of the seeds of these mistletoes.^ In the present instance, 

 however, the seeds adhered to the substratum in the usual and nor- 

 mal manner and could not have been transported in such numbers 

 by any other means than strong wind. 



In view of the fact that strong air currents are factors in the dis- 

 semination of the seeds, some consideration should be given to the 

 topograph}^ and prevailing winds of a region where mistletoe 

 abounds, as influencing the selection of seed plats (if such methods 

 are employed), the placing of strip cuttings, and even of nursery 

 and transplant beds. On a previous page, the tender age at which 

 coniferous seedlings are liable to infection by mistletoe is indicated, 

 so that the above statement regarding nursery sites is not merel}^ a 

 conjecture. Since considerable time elapses between the actual 

 penetration of the primary sinker and the time the infection becomes 

 conspicuous, three years in some instances, it is quite possible for 



^ In Bulletin 317 of the U. S. Department of Agriculture, page 24, the writer pub- 

 lished a footnote on the role of birds and animals in the distribution of the seeds of these 

 mistletoes. Since this publication was issued additional observations show that the seeds 

 are probably more widely distributed by this means than was formerly believed. A rumor 

 has been long extant that grouse feed upon the mistletoes. This has recently been verified 

 by the writer by finding in the crop of a grouse the mature seeds and plants of the 

 Douglas flr and larch mistletoes. Mr. Donald Morrison, an old, experienced hunter resid- 

 ing in the mountains near Missoula, states that grouse in the late fall, with the coming 

 of the winter snows, make a practice of congregating in the dense houselike brooms of 

 the Douglas flr mistletoe. Mr. Morrison states quite positively that these birds feed upon 

 the plants and mature seeds of these parasites when other forms of food become scarce. 



