PREFACE. 



The present treatise forms a continuation of my previous 

 work intitled „The circulation of water in the soil of the Odessa 

 Experiment Field" which first appeared in the „Review of 

 experimental Agronomy for 1904 and later in 1907 in the 

 form of a separate pamphlet based upon my report in the 

 Odessa experimental field. 



When the material, gathered up to 1904, concerning 

 soil humidity was subjected to analytical investigation, many 

 sides of the question were not then so clear so they are at 

 present. The intimate relation between the phenomena of plant 

 growth and soil humidity, their dependence one upon the other, 

 was so apparent that it was scarcely possible to work upon 

 one question without entering upon the related study of the 

 other. Commencing my investigations into soil humidity in 1895, 

 I found myself obliged in 1897 to take up the study of the 

 morphology of root-systems as applied to our cultivated plants — 

 their dimensions, the tendencies of roots of different orders, 

 and their distribution in the soil. So that it was not until the 

 year 1904 that 1 felt myself on firm ground and from that 

 time up to 1909 in a position to clear up the most impor- 

 tant points of that Section forming the subject of my treatise 

 „The root-system of cultivated plants of one year's growth" 

 which was published in the same year (1909). In this way 

 both questions — soil humidity and root-system both recei- 

 ved parallel investigation from 1895 to 1909, a period, of 

 fifteen years. 



It was natural, of course, that certain phenomena con- 

 cerning the circulation of water in the soil could not become 

 clear to me, until I had grasped the part played by root- 

 systems in that process. 



And as drought entirely depends upon certain laws of 

 water distribution in the soil and the lack of water in cer- 



