THE WESTERN VALLEYS 133 



large degree their preference for distinctly mesophytic situa- 

 tions. With respect to its particular qualities, the statement may 

 be made as follows : 



The positive elements in the nature of the arbor vitae are 

 found largely in its seeding habits. The tree produces an 

 abundance of seed throughout a long life. The seeds show a 

 high germination response, and find a suitable substratum on 

 the mossy litter of the moist forest floor. The seeds are the 

 lightest of any produced by our coniferous species and are easily 

 distributed. The arbor vitae is very tolerant and is not very 

 partial as to soils. It is little subject to serious disease. 



The principal negative elements in the composition of this 

 species are its strict moisture requireraents, its limited tempera- 

 ture range, its slow growth in its earliest years and its suscep- 

 tibility to injury by fire. 



It is evident that the positive qualities of the species out- 

 number those of a negative character, but the moisture limita- 

 tions are locally important to a degree sufficient to outweigh 

 all other considerations. It frequents river bottoms and moist 

 flats, stream banks, the bottoms of canyons and the borders of 

 high lakes in the Rocky jMountains, but in the Coast Mountains 

 of Oregon, where precipitation is ample it occurs plentifully 

 on mountain tops and stony ridges. In ilontana it is found 

 mostly in the northwestern part of the State and neighboring 

 regions, and is most aboundant, in the cooler, moisture sections 

 of the north, as on the flats below Lake IMcDonald and elsewhere 

 in the Glacier Park, and the tributaries of the Kootenai. Fine 

 stands of this tree are pictured by "Whitford and Lindgren about 

 the lakes and in the creek bottoms of the ]Mission and Clearwater 

 Mountains. It forms a conspicuous understory in some parts of 

 the white pine forests of the Priest River Valley where the 

 writer observed it in 1910. It reaches its best development 

 within the limits of moderate temperatures where the soil is 

 perennially moist. The seasonal temperature range must be 

 usually from about -35 to 100 degrees or more but with the 

 usual upper limits of summer heat at 85 or 90 degrees. 



In the case of the arbor vitae one seldom finds many small 

 seedlings, such as usually are to be found under hemlocks. The 

 growth of seedlings at first is very slow, rising to a height of 



