62 Journal of Agricultural Research voi. m, no. i 



bean, 1.42; select Grimm alfalfa, 1.48; yellow-flowered alfalfa, 1.5 1; 

 purple vetch, 1.64; and unselected Grimm alfalfa, 1.69. 



The native plants show a range in water requirement greater even 

 than the cultivated crops. Amaranths, buffalo and grama grasses, 

 purslane, and Russian thistle have a low water requirement and com- 

 pare favorably with millet and sorghum, while sunflower, fetid marigold, 

 western ragweed, and western wheat-grass have a high water requirement 

 about equal to that of alfalfa. 



Representing the water requirement of tumbleweed (Amaranihus 

 graecizans) as unity, the water requirement of these native plants is as 

 follows; Purslane, 1.05; pigweed, 1.07; buffalo grass, i.n: Russian 

 thistle, 1. 21 ; buffalo and grama grasses, 1.40; cocklebur, 1.56; gumweed, 

 2.20; mountain sage, 2.22; sunflower, 2.56; narrow-leaved sunflower, 

 2.80; lamb's-quarters, 2.89; fetid marigold, 3.18; western ragweed, 3.42; 

 western wheat-grass, 3.89. 



Varieties of the same crop often differ widely in water requirement. 

 In the case of barley, the variety having the highest water requirement 

 was 8 per cent above the lowest ; oats, 1 1 per cent ; wheat, 1 8 per cent ; 

 proso, 27 per cent; com, 31 per cent; vetch, 35 per cent; alfalfa, 48 per 

 cent; sorghum, 60 per cent; and millet, 70 per cent. This wide range 

 in water requirement among the varieties of many crops encourages the 

 belief that strains may yet be secured which are still more efficient in the 

 use of water than those now grown in dry-land regions. 



LITERATURE CITED 

 Abbot, C. G. 



1911. The silver disk pyrheliometer. In Smithsn. Misc. Collect., v. 56, no. 19, 

 10 p., I pi. 



• and FowLE, F. E. 



1913. Volcanoes and climate. In Smithsn. Misc. Collect., v. 60, no. 29, 24 p., 



Briggs, L. J. 



1913. A mechanical differential telethermograph and some of its applications. 

 In Jour. Wash. Acad., Sci., v. 3, no. 2, p. 33-35, i fig. 



and BELZ, J. O. 



1910. Dry farming in relation to rainfall and evaporation. U. S. Dept. Agr. Bur. 

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1913. Evaporation in the great plains and intermountaia districts as influenced 



by the haze of 1912. In Jour. Wash. Acad. Sci., v. 3, no. 14, p. 381-3S6. 



and Shantz, H. L. 



1913a. The water requirement of plants. I. — Investigations in the Great Plains 

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 Collins, G. N. 



1914. A drought-resisting adaptation in seedlings of Hopi maize. In Jour. Agr. 



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