1922] THONE—STARVED ROCK 353 
diurnal data were obtained. From August 6 until September 20 
readings were made every forty-eight hours. 
Discussion 
SOIL MOISTURE (figs. 1, 2).—It is obvious that topography can- 
not affect the availability of soil water for plant growth until two 
other factors have operated. The first of these, the amount and | 
distribution of precipitation, is climatic, and thus affects all loca- 
tions about equally. The second factor (or more properly group of 
factors) is strictly edaphic, having to do with the effect of the 
mechanical makeup of the soil (size, arrangement, and packing of 
soil particles) upon the capacity of the soil to absorb and hold 
precipitation water, and to deliver it to the roots of the plants 
when they demand it. Finally, the topography is of importance in 
its effect upon such factors as run-off, subsurface drainage, and 
exposure to factors that influence evaporation, both from the 
surface of the soil itself and through plant transpiration. 
The -effects of the climatic factors are plainly evident in the 
general conformity of all the curves in the soil moisture graphs, both 
those representing the growth water (fig. 1) and those representing 
the results of the operation of the Livingston-Koketsu soil points 
(fig. 2). After the cessation of the spring rains in early June, and 
until their resumption in early September, the season was one of the 
hottest and driest summers on record in recent years. There was 
but one brief period of precipitation, heavy rains occurring during 
the first few days of August. The soil water percentages show a 
notable correlation between the rainfall distribution and the water 
content of the soil at all the stations. Beginning with moderate 
but varying amounts during the late spring rains, all stations showed 
a falling off throughout June, increasing in amount and rate of loss 
through the July drought, and ending in a sudden increase at the 
time of the early August rain. Following this was another sharp de- 
crease throughout August, until a period of rains in early September 
brought a rise, somewhat resembling, that of early August, but less in 
amount. Fair weather during th period of the season 
brought the beginning of another decrease. The ready responses 
of the curve to both drought and rain are very notable features. 
