Studihs on Crown Gall oi Plants 417 



1918, when Innkholdcr annouiKcd tins in P/.)yto(hi/bology,-'* a 

 multiple factor hypothesis would have found its way also into 

 the literature, and more than the two factors of resistance and 

 susceptibility would be necessary to explain all of the phenomena 

 in breeding, at least to the minds of some authors. By 1918 Phyto- 

 pittljology and other journals would have published many articles, 

 abstracts, and notes relative to breeding disease-resistant plants. 

 Smith estimated as of especial importance J. A. McClintock's study 

 of " Spinach blight." -" He said of this in his address, " Fifty 

 Years of Pathology: " '" "' In 1918 McClintock and L. B. Smith 

 published on a destructive mosaic blight of spinach and showed 

 that it is not only transmitted by aphids, but also from one 

 generation of aphides to another. L. B. Smith (1920) bred spinach 

 resistant to this, disease." 



Not less irnportant than breeding for resistance to disease and 

 cold and for increased productivity and improved qualit)' was 

 breeding for resistance to alkali and to drought. To illustrate 

 the Department's work, Smith at the Genetics Conference of 1906 

 selected alfalfa and wheat as the crops and described first the 

 program of bringing into cultivation western areas of alkaline 

 lands by introducing " certain types of leguminous and other 

 plants " more tolerant of alkali than ordinary plants. Part of 

 this work w^as in charge of one of Dr. Webber's assistants, T. H. 

 Kearney, known also as an agricultural explorer and for valuable 

 cotton importations from Egypt. Next Smith told of the nation's 

 westward extension of its wheat belt into areas formerly pasture 

 or unoccupied lands, plains, or deserts by introducing durum 

 v.heats from Russia. This was the triumph of Mark Alfred 

 Carleton, in charge of the Department's office of cereal inves- 

 tigations. In semi-arid states of the central west and west where, 

 though soil was adapted to wheat-growing the rainfall had been 

 insufficient to bring winter and spring crops to maturity, the 

 drawback of climate had been overcome, and immensely valuable 

 industries, including the famous macaroni wheats, been either 

 established or extended. Again without sacrificing scientific con- 

 tent or permitting his audience to go unacquainted with the facts 



" 8(7) : 353, July 1918, and authorities cited; Fifty years of pathology, op cit., 37. 

 " Phytopathology 8(2): 74, Feb. 1918. 

 " Op. cit., 37. 



