■576 Journal of Agricultural Research voi. iv, no. 3 



actual fertilization of the mistletoe takes place, those tissues destined to 

 become the seed are, in infected plants, observed to be completely filled 

 or destroyed by the mycelium of the fungus. After infection, the young 

 seed capsule never increases much in size and is entirely dominated by 

 the parasite. The diseased capsules usually fall away during late winter 

 and early spring, which allows time for the infection of the pistillate 

 plants. The drain on the vigor of the mistletoe plant, if all the young 

 capsules are infected, is such that it may also succumb and fall. If only 

 one or two capsules of the plant are infected, it will remain intact, 

 maturing the uninfected fruit of the season and fruiting again the follow- 

 ing year. Usually, however, the infection of all the fruits of a mistletoe 

 colony or of all the plants of a broom is so complete that few or no seeds 



mature. 



ECOLOGY 



All collections so far made of the fungus have not been at an elevation 

 much greater than 3,600 feet, although its hosts may range well up toward 

 the timber line. This indicates a preference for the conditions of the 

 lower levels, where it is not so much exposed to fluctuations of warmth 

 and moisture. The latter factor is probably of greater influence. Until 

 the fungus is found elsewhere it may be said to prefer the North Tem- 

 perate regions. Forestburg, N. Y., its first known station, is about on 

 a line with the Upper Peninsula of Michigan, the region of its second dis- 

 covery, and northern Idaho, where it was last found. This is its geo- 

 graphical and climatic range at present. Developing either on exposed 

 or shaded plants, the fungus seems to favor those growing in shaded 

 positions, such as the inner parts of brooms. Absence of direct sun- 

 light may promote development, but, after the capsule becomes infected, 

 direct sunlight can not have much influence on the maturing of the 

 fungus. The germination of the spores would probably be promoted by 

 an absence of direct sunlight. Warm fall rains, such as occur in northern 

 Idaho, are undoubtedly very favorable to the development and spread 

 of the disease, since in this region the fungus has been found most abun- 

 dant. In damp river bottoms or on the borders of swamp areas the lodge- 

 pole-pine mistletoe, which frequently occurs in profusion in such a habi- 

 tat, is very likely to be attacked by the fungus. Prof. Peck ^ does not 

 record the conditions under which the fungus was growing at Forest- 

 burg, N. Y., but presumably it w^as a region of considerable humidity. 

 The Upper Peninsula of Michigan, where Prof. Wheeler collected the 

 fungus, is a region of numerous swamps and abundant atmospheric 

 moisture. In view of the fact that the fungus is parasitic on the rather 

 succulent capsule of the mistletoe, atmospheric humidity should not 

 greatly interfere with its life functions, except probably in the initial 

 stages of spore germination. The fungus should thrive on the larch 



iPeck.C.H. Op. dt. 



