266 THE SMALL GRAINS 



lies between east and southeast. In the accompanying 

 maps (see Figs. 75-77) these directions of climatic resist- 

 ance are, very roughly, indicated by arrows. Sometimes 

 evaporation becomes so great that it must be considered 

 as an additional factor (282). 



280. Water requirements of cereals. Under the 

 heading transpiration (27), some of the benefits resulting 

 to the plant through that process are mentioned, but 

 also the fact that the loss of water often becomes serious. 

 This loss is so great in semi-arid districts in addition to 

 light rainfall, that the one great problem is the water 

 supply. 



In Wisconsin it was determined by King that barley re- 

 quired 392.9 tons of water to produce 1 ton of dry mat- 

 ter, and oats 522.4 tons. Hellriegel found that barley 

 used 310 pounds of water for each pound of dry matter 

 produced, spring rye 353 pounds, oats 376 pounds, spring 

 wheat 338 pounds, and buckwheat 363 pounds. Such 

 variation in the water requirement of different crops 

 shows the importance of elaborate experiments in this 

 line under dry conditions as an aid to the selection of 

 crops for dry lands. 



281. Experiments of the United States Department of 

 Agriculture. Experiments of the kind above men- 

 tioned were conducted by Briggs and Shantz (1913, 

 1914), with most interesting results, and form a fitting 

 companion work to that on the wilting coefficient for 

 different plants. Results of the latter investigations show 

 the water efficiency of different soils, while results of the 

 former show the water efficiency of different crops. 

 In these investigations, there was found to be great varia- 

 tion in the water requirements, not only of different 

 cereal crops, but also in those of different varieties of 



