374 Journal of Agricultural Research voi. iv. no. 3 



and 8 mm. n. a. 0.65 apochromatic objective) show a close uniformity 

 to those of the type material. The measurements of the asci from fresh 

 material range as follows: 22.3, 22.8, 24, 24.4, 24.8, 25.2// in length. 

 Evidently considerable shrinkage takes place in stained material, the 

 stained asci measuring 16.5, 16.9, 19.8, 21.9/^ in length. The average 

 breadth of the ascus is 3/^. The ascus contains eight unicellular, globose, 

 thick-walled spores. The spores are at first hyaline, but nearing maturity 

 they assume a very conspicuous brown-black color. The color of the 

 mature spores is assumed after their escape from the ascus. The pre- 

 liminary color changes may, however, take place within the ascus. 

 Prof. Peck, in his original description, states that the spores are hyaline; 

 still he represents, in his illustration (PI. LV, fig. 14), four mature spores 

 which are black. The change from a hyaline to the pronounced brown 

 or black color was evidently recognized,, since "an ascus containing 

 young spores" is represented, after which "four mature spores" that 

 are black are represented. An examination of some of the type material 

 kindly sent the writer by Mr. H. D. House shows the spores in all stages 

 of development and varying from hyaline to black. The dimensions of 

 the spores in the type material are found to agree with the measurements 

 of the spores in the western fungus, which range as follows: Unstained 

 and out of ascus, 3.7, 4.5, 4.9, 5.3, 5.8, 6.2/£; stained, 4.1, 4.5, 4.9, 5.3, 

 6.2/z. Previous accounts give the diameter of the spores as "about 4/i." 

 The paraphyses are filamentous, short, and very inconspicuous. 



All the asci of a single perithecium do not mature their spores together; 

 instead, at the time mature spores are escaping from the perithecium, 

 young asci showing early stages of spore differentiation are discernible. 

 There is consequently a gradual dissemination of the spores, governed 

 to an extent by the humidity of the atmosphere. The opening through 

 which the spores escape is directly at the apex and is formed by the free 

 ends of the thick-walled hypha composing the walls of the perithecium. 

 The cells composing the tips of these hyphae seem to possess certain 

 hygroscopic properties, as they are observed to bend in or out on the 

 addition or absence of moisture. 



BIOLOGY 



In what manner the spores of W. arceuthobii are conveyed to the 

 pistillate flower of the mistletoe in nature the writer is not in a posi- 

 tion to state definitely. Since isolated infections occur promiscously 

 on different branches of the same tree or on different trees in the same 

 locality, it is evident that the wind is the chief factor in spore dissemina- 

 tion. A fact observed among the infected plants on lodgepole pine of 

 the swamp area previously mentioned supports this view. The area 

 lay with its long axis in the direction of the prevailing winds of the Priest 

 River Valley. An examination of the trees bearing infected plants 

 showed that thev were more or less in line with each other and extended 



