New York Agricultural Experiment Station. 401 



covery that resistance and susceptibility in one species are Men- 

 delian characters. He has found that susceptibility in wheat to 

 attacks of yellow rust are inherited in Mendelian ratio. If his 

 conclusions are correct, susceptibility to this rust is a unit- 

 character in wheat; immunity depends upon the absence of this 

 character. 



BifTen's evidence is such that we are forced to accept it for 

 this disease of wheat. When we supplement his discovery with 

 the knowledge we previously had of inheritance of disease, we are 

 filled with hope that immunity and susceptibility are inherit- 

 able characters with many diseases of plants. 



It will not do to jump immediately to the conclusion that we 

 shall shortly breed fruits resistant to all fungi and bacteria. 

 The task will be long and laborious for any one disease, as it can 

 be accomplished only by breeding new varieties — old sorts cannot 

 be changed. Varieties having immunities must be crossed with 

 other varieties. With the manifold characters of the two parents, 

 it may require much shuffling and many draws to secure the com- 

 bination of disease resistance with other characters that a good 

 variety must have. 



Meanwhile, not much real building can be done until we have 

 the foundation laid. That foundation must be knowledge of the 

 immunities and susceptibilities of existing varieties. The chief 

 object of this brief discussion of resistance to disease is to intro- 

 duce a list of varieties of apples which at the Geneva Experiment 

 Station are more or less resistant or susceptible to two diseases — 

 apple scab (Venturia inaequalis [Cooke] Aderh.) and apple blight 

 (Bacillus amylovorus [Burr.] De Toni). 



Susceptibility of Apples to Apple Scab. 



Relatively immune. Relatively susceptible. 



Alexander, Belmont, 



Baxter, Bellflower, 



Ben Davis, Chenango, 



Black Gilliflower, Esopus Spitzenburg, 



Cranberry Pippin, Fall Pippin, 



Gano, Fameuse, 



26 



