DISEASE RESISTANCE IN PLANTS. 127 



resistant, but worthless commercially. He crossed this with com- 

 mercially desirable varieties. The seed resulting from this cross, 

 when planted the next year, revealed the fact that he had obtained 

 about a thousand new varieties, most of which were either worth- 

 less commercially or non-resistant. He selected a few of the most 

 promising of these for further study, and found that he had one 

 variety commercially desirable, profitable, and strongly resistant. 



"What has been done? 



Let us see what has been accomplished toward obtaining practical 

 results in the breeding or selection of disease proof varieties. I 

 will speak briefly of some of the most notable results obtained in 

 this country or applied to American conditions. It is not my 

 purpose to review the observations (and they are many) on resistant 

 varieties of vegetable or fruits that are in common use, but to con- 

 fine myself to a discussion of the outcome of definite efforts to obtain 

 varieties resistant to specific diseases. 



Wheat. 



"We will agree that to spray a wheat field for rust would be out 

 of the cjuestion from a practical standpoint, even though such 

 treatment might rid the crop of the disease. It is evident that in. 

 sections where wheat rust is especially prevalent, disease resistant 

 varieties of wheat would be of especial value. Investigations have 

 been made in Europe, Australia, and the United States for the 

 purpose of obtaining rust resisting wheats. ^Nlore or less success 

 has been obtained by all investigators. Carlton, working in this 

 country, has made a study of all available varieties from all coun- 

 tries and has found that certain varieties of the Durum wheats 

 are most resistant to the black stem rust. In this connection the 

 recent work of R. H. Biften on the hybridization of wheats bids 

 fair to have a far reaching influence on future work in developing 

 immune varieties. He found that susceptibility and immunity 

 in certain varieties of wheats are definite INIendelian characters,, 

 the former beins the dominant one. 



