Reed: The mildews of the cereals 385 



hybrids from this cross all rusted very badly, like the parent Red 

 King. However, 300 grains were secured, from which 260 plants 

 were raised in 1903. The season was very favorable for rust. 

 The plants were examined at the height of the rust attack. Sixty- 

 four were found practically immune and one hundred and ninety- 

 five rusted, most of them badly. The ratio of 64 to 195 is nearly 

 I to 3. Taken in connection with the fact that the first genera- 

 tion was badly rusted, Biffen concluded that susceptibility and 

 immunity are Mendelian characters, susceptibility being domi- 

 nant. The results for the third generation confirm this view. An 

 examination of four plots which contained both rusted and non- 

 rusted plants, showed 149 rusted plants and 48 free from rust, a 

 ratio of 3.1 to I. 



Biffen has also crossed American Club Wheat {Triticum com- 

 pacttiui) and Michigan Bronze {T. vulgare^. The former is rela- 

 tively immune, while the latter is a susceptible variety. The hy- 

 brids of the first generation were badly rusted. The seed of these 

 hybrids was planted and the following results were obtained : 



Plant 5^ yielded 56 rust-free individuals and 147 rusted individuals. 

 ** 5b ** 45 '* ** " "153 " " 



u ^c ** 47 '* ** <* " 142 *' '* 



<i ^(J ic 26 " " ** ** 154 ** " 



C< ii. 



*' 5e ** 44 '' ** *' " 164 



22S 760 



r 



Plants 5f, 5g, 5h, and 5j, gave 295 rust-free plants and S49 

 rusted. The whole series gave 523 immune and 1,609 ousted, a 

 ratio of i to 3.07. 



It was observed that the severity of the rust varied on the dif- 

 ferent plants. From fifty heads of badly rusted plants, .8 gm. of 

 seed was obtained ; from fifty heads of moderately rusted plants 64 

 gm. of seed; and from fifty heads of immune plants, 145 gm. of 

 seed were harvested. 



Biffen tested also the Inheritance of immunity to the attacks of 

 ErysipJie Graminis, HordeMui spontaneiim Koch and H. hexasticho-^ 

 furcatttm K.H. were crossed, the former being the immune parent. 

 The hybrid was attacked by mildew as badly as the susceptible 

 parent. In the next generation 56 plants were badly mildewed, 16 

 slightly attacked, and 7 entirely free. At the same time, the parent 

 H. spontaneiim was very slightly mildewed, while the other parent 



was badly attacked. 



