Oct. n, 1914 Water Requirement of Plants 61 



measurements in 191 2 would also indicate that the character of the 

 season influences the water requirement of some plants more than 

 others. For this reason, where the results of two or more years have 

 been combined in the table, the probable error has been confined to the 

 errors of experiment and does not include the fluctuations in water re- 

 quirement due to the season. 



In order to facilitate comparison, the plants have been arranged 

 under three main heads: Grain crops, other crops, and native plants. 

 Under "Grain crops" are also included certain sorghums and millets 

 which are usually grown for forage. Under the heading "Other crops" 

 are included principally the legumes, cucurbits, crucifers, sugar beets, 

 cotton, and potatoes, as well as some of the introduced grasses. Under 

 the heading "Native plants" are listed indigenous species, as well as 

 certain introduced species which have become thoroughly established. 



The grain crops fall rather naturally into two sections: Those of low 

 water requirement — proso, millet, sorghum, and com — and those of high 

 water requirement — wheat, barley, oats, rye, and flax. The plants with 

 a comparatively low water requirement are late-maturing crops, which 

 make their best growth during the hottest and driest portion of the 

 summer. The plants having a comparatively high water requirement 

 mature during midsiunmer and make their best growth during the earlier, 

 cooler period of the year. The range in water requirement of the first 

 group is from 261 for Kursk millet to 468 for Sudan grass, while the 

 range in the second group is from 473 for Turkey wheat to 905 for flax. 



Representing the water requirement of proso as i, the water require- 

 ment of the grain crops is as follows: Millet, 1.06; sorghum, i.io; com, 

 1.26; teosinte, 1.34; wheat, 1.76; barley, 1.83; buckwheat, 1.98; oats, 

 2.04; rye, 2.34; rice, 2.42; and flax, 3.38. In other words, flax requires 

 more than three times as much water and rice more than twice as much 

 water as proso and millet in producing a pound of dry matter. 



In the second group sugar beet ranks first, having a water requirement 

 almost as low as com. Potato ranks next, followed by crucifers, cucur- 

 bits, legumes, and grasses, in order. A wide range is shown in each of 

 these families. The groups as a whole show a range somewhat less than 

 the grain groups. 



Representing the water requirement of sugar beet as i, the values for 

 the "Other crops," exclusive of the legumes, are as follows : Cabbage, 

 1.36; Irish Cobbler potato, 1.39; watermelon, 1.5 1 ; cantaloupe, 1.57; tur- 

 nip, 1.60; cotton, 1.63; cucumber, t.8o; wheat-grass, 1.85; rape, 1.87; 

 squash, 1.89; pumpkin, 2.10; and brome-grass, 2.56. 



The cowpea was the most eflicient of the legumes. Representing its 

 water requirement by i , that of the other legumes is as follows: Peruvian 

 alfalfa, 1.14; chick-pea, 1.16; soy bean, 1.18; navy bean, 1.20; hairj' 

 vetch, 1.21; sweet clover, 1.35; Mexican bean, 1.35; horse bean, 1.36; 

 red clover, 1.38; Canada field pea, 1.38; crimson clover, 1.41; wild soy 



