121 



borders on the grass land strips of timber afforded convenient 

 material for study. In these cases the stand was a mixture of 

 yellow pine and Douglas fir, varying in height from five to 

 twenty-five or thirty feet. One of these areas occupies one slope 

 of a shallow, narrow valley which traverses in a direction from 

 southeast to northwest, the barren western slope of Mt. Sentinel, 

 southeast of the town of Missoula. The timbered slope of the 

 valley faces the northeast, its opposite slope facing southwest is 

 treeless. Along the edge of this stand, a strip over a quarter of a 

 mile in length and about fifty 3'ards in width provided the 42 

 young yellow pines whose measurements are here recorded. All 

 the pines up to thirty feet in height were measured, except such as 

 showed evidence of injury in the parts concerned. 



In Table I the height growth is shown of each of the five 

 seasons, 1909 to 1913 inclusive. The measurements are in inches. 

 It will be observed that practically every one of the pines growing 

 on this area exhibited a growth during the season of 191 1 con- 

 siderably less than that of either of the two seasons preceding or 

 following, and that, although the difference in a few cases is 

 reduced to zero, in nearly all of the individual cases the difference 

 between the growth of 191 1 and that of the other seasons 

 amounted to several inches. The same relation appears con- 

 spicuously in the totals and again in the averages, but the most 

 significant fact seems to be in the absence of exceptions to the 

 general rule. 



Table II presents the results of similar measurements on 

 another area near Missoula about two miles from the first. Only 

 a few observations were recorded in this case, as practically every 

 tree approached showed the same condition. 



If one compares these measurements with the weather data 

 given in Table III he will find that the lengths of the internodes 

 stand in relation to the conditions of the seasons in the manner 

 suggested above. The mean precipitation and temperature 



* Miyake, K. On the starch of evergreen leaves, and its relation to photo- 

 synthesis during the winter. Bot. Gaz. 33: 321-340, 1902. 



t Jumelle, Rev. Gen. de Bot. 4: 263, 1892. Pfeffer's Physiology of Plants, 

 Vol. I, p. 338. 



t Green, J. R. Vegetable Physiology, p. 174. 1911. 



