tain soil -belts, so with the „ Nature of drought" — its chara- 

 cteristics appear when studied in connection with types of soil 

 approaching that of the Odessa experinnental field a choco- 

 late colored clay containing from 3 to 6 per cent of manure. 



However, the attention of the reader of my results may 

 be transferred to all blackearth soils resting on beds of fi- 

 brous clay such as the Russian steppe belts of the south and 

 the black-earth governements of the East. 



During the last two years 1 have demonstrated the dia- 

 grams of the annual course of humidity embodied in this 

 treatise to very many people attending the Odessa experi- 

 ment field. They all insisted upon the quickest possible publi- 

 cation of my results, but it is only lately that all the details 

 of the desired work have fully developed. Circumstances outside 

 my control have hurried the publication of this work so that 

 certain parts lack somewhat in completeness. I consider it my 

 duty to express my thanks to the former supervisor of the 

 meteorological station on the Odessa field, K. N. Verzilow, 

 who gave me m.uch assistance in investigation soil-humidity 

 of root-systems. 



y. I^ofnj/sfrow. 



