UTAH ACADEMY OF SCIENCES 261 
hand because continuous records are not available. How- 
ever, Shreve® has shown that in physiological plant geog- 
raphy, where soil moisture data are not available, the 
annual and seasonal distribution of precipitation has been 
used to good advantage as criteria of soil moisture and in 
conditioning the distribution and growth of various types 
of vegetation. 
Mr. F. S. Baker and the writer‘ have found that the 
seasonal amount and distribution of precipitation is of 
unusual importance as a factor limiting the distribution 
of western yellow pine ( Pinus ponderosa and P. ponderosa 
scopulorum) in the Great Basin. Douglass® has found 
that the width of the annual rings is a reliable index of 
rainfall and that double rings are indicative of the distri- 
bution of precipitation throughout the year. The writer® 
in a symposium on site classification, pointed out that the 
majority of foresters recognize relative height growth of 
young trees as a more sensitive indicator of the quality 
of habitat than diameter growth or any other single 
criterion. 
Kirkwood,’ in seeking evidence on the relation of the 
growth of western yellow pine and Douglas fir (Pseudo- 
tsuga taxtfolia) to the distribution of rainfall, made a ser- 
ies of measurements in the vicinity of Missoula, Montana. 
After correlating the current annual growth of fifty wes- 
tern yellow pine and twenty-three Douglas fir saplings 
3Shreve, Forrest. Rainfall as a Determinant of Soil moisture. 
The Plant World 17: 9-26. 1914. 
4The report of this investigation is awaiting publication. 
5Douglass, A. E. A Method of Estimating Rainfall by the 
Growth of Trees. Bulletin American Geographical Society 46: 321- 
335. 1914. 
Climatic Cycles and Tree Growth: A study of the annual 
rings of trees in relation to climate and solar activity. Pub. 289, 
Carnegie Institution of Washington, 127 pp., 40 figs., 12 plates. 
Wash,, D.C. 1919. 
6Korstian, Clarence F. Native Vegetation as a Criterion of 
Site. The Plant World 22: 253-261. 1919. 
7Kirkwood, J. E. The Influence of Preceding Seasons on the 
Growth of Yellow Pine. Torreya 14: 115-125. 1914. 
