VOLUME LVIII 



NUMBER 3 



THE 



Botanical Gazette 



SEPTEMBER 1914 



EVAPORATION AND SOIL MOISTURE IN RELATION TO 



THE SUCCESSION OF PLANT ASSOCIATIONS 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 191 



George Damon Fuller 



(WITH TWENTY-SEVEN FIGURES) 



I. Evaporation 



The water conditions of plants have long been recognized by 

 ecologists to be matters of the highest importance, but unfortu- 

 nately it has seldom been possible to describe these conditions in 

 other than the most general qualitative terms. The only factor 

 affording quantitative data has been precipitation, and this is 

 only indirectly related to plant production on account of the many 

 irregular variations that exist between the amount of rainfall and 

 the quantity of water available for plant growth. In* a general 

 way, and especially in dealing with large areas, a fairly close rela- 

 tionship may be established, but within the different habitats of 

 a single region no such connection can be recognized. 



In a study of water conditions, two phases of the subject are of 

 importance. They are the direct source and amount of the supply 

 and the region and cause of the loss. The latter is a climatic, the 

 former largely an edaphic, problem, for it is evident that plants 

 derive their moisture from the soil and lose it into the air, and for 

 the quantitative solution of these problems it is necessary to meas- 

 ure the power of the air to extract water from the plant; in other 



193 



