117 



ative activity is well known. It is equally well known that the 

 rate of height and diameter increase is the expression of the 

 relative abundance of soil moisture, as well as of other elements 

 in the essential conditions of growth and development. It has 

 been shown that there is a close relation between the annual 

 precipitation and diameter growth in the western yellow pine. 

 Douglas,* working on Pinus ponderosa near Flagstaff, Arizona, 

 found that for a period of years the relative diameter of each 

 season, as revealed by careful stem analyses, corresponded closely 

 with the relative abundance of moisture in the several years, as 

 shown by the weather records of that locality. The results of 

 this investigation further showed that the variability in increment 

 was in this instance subject to several factors, such as the relative 

 porosity of the subsoil, the unequal distribution of soil moisture 

 in different directions from the tree, etc. ; in short, that any dif- 

 ferential distribution of moisture, either topographically or from 

 season to season was expressed in a corresponding variation in 

 the size and form of the annual rings. The conclusions in this 

 paper seem to be supported by the facts presented, and will 

 doubtless apply to other regions as well, where the amount of soil 

 moisture varies considerably from year to year during the period 

 of more rapid growth. Relative height and diameter increase, 

 however, are not always the expression of the conditions in the 

 same season in which such increase took place, but sometimes 

 indicate the factors prevailing in the preceding year. Bogue,t 

 as a conclusion from observations at Stillwater, Okla., states that 

 "the month of maximum rainfall is the month of maximum 

 growth." As a result of further studies at Lansing, Mich., he 

 finds that the width of the ring is proportionate to the rainfall 

 within certain limits, but that excessively heavy or light pre- 

 cipitation is evidenced by a corresponding growth of the tree in 

 the following year, and rightly attributes the difference to the 

 difference in the amount of food material stored in the preceding 

 season. 



* Douglass, A. E. Weather cycles in the growth of big trees. Monthly 

 Weather Review 37: 225-237, June, 1909. 



t Bogue, E. E. Annual rings of tree growth. Monthly Weather Review 33: 

 250-251, June, 1905. 



