HISTOEY OF THE INVESTIGATIONS. ^ 9 



will notice that some individual plants of a variety are markedly 

 more resistant than other plants from the same lot of seed growing 

 beside them. This fact gives the plant breeder an opportunity to 

 produce still more resistant strains of the drought-resistant varieties 

 by the persistent selection of such individual plants. 



Other qualities of the plant must not be neglected in breeding 

 forage plants for drought resistance. The quantity and quality of 

 the hay and seed are equally im})ortant. The individual plants 

 which are actually most drought resistant may be deficient in yield 

 and quality and will have to be discarded in favor of other individuals 

 of somewhat less drought resistance but in other respects superior. 

 Good seed production is essential not only in species that are grown 

 primarily for the seed, but in those which are grown for hay, since in 

 order to keep the variety drought resistant it is necessary that the 

 seed should be produced in the region to which it is adapted. For- 

 tunately the yield and quality of the seed are generally better in 

 semiarid than in humid regions. This is notably the case with 

 alfalfa, of which most of the commercial seed at present grown in the 

 United States is produced under irrigation and consequently is not 

 the best adapted to dry-land agriculture. 



In perennial plants like alfalfa and the principal meadow grasses, 

 hardiness or resistance to winterkilling is another essential charac- 

 teristic, especially in the nortliern part of the Great Plains. Early 

 maturity is of great importance in the growth of annual crops. One- 

 half of the annual precipitation in this region occurs from April to 

 July, inclusive. It is therefore desirable to obtain early-maturing 

 strains which will make most of their growth during the period when 

 the soil contains its greatest amount of moisture. In the northern 

 part of the Great Plains the development of locally adapted varieties 

 of sorgos, nulos, and other late-maturing crops is hindered by the 

 shortness of the season. In breeding these plants the ability to ripen 

 seed as early as possible is a characteristic that can not be overlooked. 



HISTORY OF THE INVESTIGATIONS. 



The plant breeding for drought resistance described in this paper 

 is a continuation of the work begun by Prof. W. A. ^Vheeler in 1904 

 at the Highmore substation of the South Dakota Agricultural Ex- 

 periment Station. Professor Wheeler was at that time botanist of 

 the South Dakota station. The writer was associated with him as 

 student assistant in botany and was in close touch, almost from the 

 beginnmg, with the plant-breeding work carried on under his direc- 

 tion. In the breeding work at ITighmore all the ])rincipal forage 

 crops of the region were taken up, alfalfa, clover, millet, sorghum, 

 smooth brome-grass (Bromus inennis), western wheat-grass (Agro- 

 58575°— Bui. 196—10 2 



