m 



324 BOTANICAL GAZETTE [november 



With the geotome were carried to the laboratory in Boulder in tightly 

 dosed tin cans and weighed as soon as possible after collection. 

 They were then opened^ the samples dried for three days at an average 

 temperature of 24 to 29''C., after which they were weighed again. 

 The difference between the two readings gave the weight of moisture 

 contained in the soil, and this weight is expressed in per cent, of weight 

 of the dried sample. In the case of soil samples which it was necessary 

 to carry in the pocket for several days before weighing, an allowance 

 of a few decigrams must be made, since there was a slight evaporation 

 from the tins. This slight inaccuracy, however, is not sufficient to 

 invalidate the general results. " 



At each station soil temperatures were taken on the surface of the 

 ground and at depths of 11.25*^'^ and 22. 5^"^, respectively. The 

 air temperature was taken at 7.5^^ and 9*^^ above the ground; 

 while humidity readings were also taken at 7.5^"^ and 9"^"" above the 

 surface. Occasionally humidity and temperature readings at 1.8 

 above the ground were taken. 



The light readings in each formation were obtained with the pho- 

 tometer, and these were evaluated in terms of a standard series of ten 

 readings of one to ten seconds respectively, taken at 12:30 P. M. on 

 October 2 at 1620^^ altitude in Boulder. A similar series was taken 

 at noon on June 23, but unfortunately lost. 



The aneroid barometer was used in obtaining the approximate 

 altitudinal limits of the formations, and the altitudes so obtained 

 were checked whenever possible by those obtained by the United 

 States Geological Survey. 



The obsen^ation stations were chosen at points as nearly typical 

 as possible for each formation, and at most stations from three to 

 many obsen'-ations were taken during the summer of 1905."^ Where 

 the formations showed isolated societies within their limits, separate 

 stations were selected for each of these. 



Boulder County, Colorado, lies on either side of the fortieth paral- 

 lel of north latitude. Its western boundary is the Continental Divide 

 of the Rocky Mountains, while to the east it extends about 19^"^ 

 from the base of the mountains. With the exceDtion of the banks 



mountains 



4 Three obsen-ations were taken in 1907 as noted below. 



