32 BOTANICAL GAZETTE [JANUARY 
ina small plat. Round this plat five other varieties of wheat 
were sown, also in small plats, all these varieties being well | 
known for several years as very little susceptible to yellow rust. — 
On May 11 the middle plat showed traces of yellow rust. After i 
thirty-three days the rust had increased a little, and after ten _ 
days more the rust had reached its maximum, the greatest 
degree of destruction. But at the same time all the surround- ; 
ing plats at the end of the thirty-three days were clean, and at — 
the end of the following ten days two plats still continued quite © 
clean, and the other three only showed small traces of rust. All” 
the plats were sown on the same day, and the weather during 
the last part of May and the beginning of June was part of the- 
time very rainy. a 
Here we have an example of what is usually called the dif e 
ferent susceptibility of varieties to disease. Such a different 
predisposition for yellow rust we have up to this time been able- 
to point out with certainty in different varieties of wheat and 
barley. In view of observations made during the summer of 
1896, I have reason also to suspect such a predisposition in the 
different varieties of wheat for brown rust, a kind of rust, how-_ 
ever, that has but subordinate practical interest in Sweden. 
Sometimes we find only a slight propagation of rust, even | 
between different individuals of the same wild grass. I have | 
observed specimens of Festuca elatior badly attacked by Puccima — 
or specimens of Brachypodium silvaticum attacked by P. Bary 
among completely healthy ones. 
3. Lhe germinating power of the uredo- and ecidiospores is ofte 
small, or at best capricious. 
The fact that the yellow rust in wheat shows so little trams- 
mission from one variety of wheat to another has led to making: 
the germination of summer spores (uredo- and zcidiospores 
the subject of special investigation. It appears that in certail 
kinds of rust these Spores are uniformly very capricious in thet 
germination, and even sometimes absolutely refuse to germinate 
