pe OS oP ee 
VOLUME L NUMBER 4 
BOTANICAL °° GAZETEEe 
OCTOBER 1910 
RELATION OF SOIL MOISTURE TO DESERT 
VEGETATION: 
BuRTON EDWARD LIVINGSTON 
(WITH FOUR FIGURES) 
IntRopuction.—Of a number of lines of study now in progress, 
looking toward some quantitative knowledge of the relation obtain- 
ing between vegetation and environmental conditions, the determi- 
nation of the march of soil moisture at Tucson has now progressed 
sufficiently far to warrant publication. The present paper deals 
with a continuation of the data upon soil moisture published by 
the writer under the title: ‘“‘The soils of the Desert Laboratory 
domain” in SpaLpING’s recent monograph on desert ecology (1). 
The data there presented comprise observations on soil moisture 
content extending over the period from October 1907 to April 
1908. The period of observation has now been extended to March 
1909, thus including both the spring dry season and that of the 
summer rains. To make the present presentation complete, the 
observations already published are here included. 
RELATION OF SOIL MOISTURE TO OTHER FACTORS.—Just as the 
evaporating power of the air and the nature of the transpiring 
organs practically determine the water requirement of plants, so 
do the soil moisture content and the nature of the root system 
‘determine the water supply. Aside from those cases (of toxic 
soils and soils of high osmotic pressure) where the nature and 
amount of the solutes in the soil solution exert an influence upon the 
character of the root system or upon the rate of water absorption 
— * Publication from the Botanical Laboratory of the Johns Hopkins University, 
je 16, : 
241 
