28 EDITH SCHWARTZ CLEMENTS 



far the most important. It is coming to be generally admitted that 

 the chemical and physical properties of the soil are of importance 

 chiefly in so far as they affect the amount of available water, the 

 former through varying amounts of salts and the latter through the 

 ease with which the particles give up water. In this connection it 

 is important to note that gravel will yield all but 0.5 per cent, of its 

 water, while clay retains 8 per cent. Consequently the water in the 

 soil at any given spot must be considered with reference to the 

 available and not the absolute amount. 



The methods for measuring physical factors as laid down in 

 Clements' Research Methods in Ecology were those applied in 

 carrying on the present investigations. On account of the dif- 

 ficulty of covering the large area represented the records are for 

 some regions more or less fragmentary and unsatisfactory. It is 

 hoped, however, that these may be made good by future investiga- 

 tions, and the present results, though incomplete, are to be looked 

 upon as a step at least in the right direction. The records which 

 follow were obtained during the summers of 1903 and 1904. 



LIGHT. Light readings to the number of no were made during 

 the two summers by means of the simple photometer. It was found 

 that full sunlight is equally strong throughout the regions, and not 

 more intense for high altitudes, as is generally supposed. The light 

 values in the following table are the noon readings of the various 

 situations expressed in terms of the meridional sunlight of Septem- 

 ber 12, 1904, at the subalpine station. 



WATER-CONTENT OF THE SOIL. During the two summers 180 

 records were made throughout the region. The average of those 

 taken in a particular soil or locality is given in the table under 

 " normal water-content." The saturation point of different soils 

 was also obtained, as well as the available water. The latter was 

 determined by measuring the percentage of water left in a soil con- 

 taining plants at the wilting point. The percentages are based on 

 the moist soil and are, in consequence, a little lower than they 

 would be if figured with reference to the dry weight. 



HUMIDITY. Continuous records of humidity were made in the 

 foot-hills and in the spruce forest and gravel slide of the subapline 

 region by means of automatic psychrographs, during eight weeks of 

 1904. Readings were made twice daily for the brook bank and 

 half gravel formations of the subalpine region in 1904, and single 

 readings were taken frequently throughout the two summers at a 



