36 A STUDY IN CEREAL RUSTS 



ous with but little difference between the two series. There seemed to 

 be a tendency for the mycelium to spread more in the plants grown in 

 wet soil, but the pustules were not larger than those on dry-soil plants. 

 Whatever difference there was appeared as a slightly greater virulence 

 on the wet-soil plants. 



It will be noticed that lumillo and Kubanka, drought-resisting 

 plants, were more severely attacked when grown in dry soil. Minne- 

 sota No. 163, on the other hand, a mesophyte, did not show so much 

 difference. It is probable then, that, conditions having been favorable 

 for a rust infection, the water relation in the soil which is most favor- 

 able for the host plant's development is also the most favorable for the 

 development of the rust. It seems probable also that in at least some 

 forms it is not the water content of the soil which predisposes grains 

 growing in low places to rust but rather the increased relative humidity 

 which enables the rust spores to germinate and infect the plants. The 

 temperature in such places also probably exerts an influence. This is 

 pointed out by Freeman and Johnson (1911, p. 65) in connection with 

 the rust epidemic of 1904. 



EFFECT OF FERTILIZERS 



In the first series the varieties used were : Minnesota No. 163, 

 Arnautka 288, Khapli, emmer 1522, lumillo 1736, einkorn 2433, and 

 Kubanka 2094. Some were planted in ordinary rich loam, others in 

 rich loam plus fresh barnyard manure, and a third series in rich loam 

 to which barnyard manure and bone meal had been added. Especial 

 care was taken to keep all plants under the same conditions of tempera- 

 ture, moisture, and light both before and after inoculation. 



On the wheat plants which were grown on very heavily fertilized 

 soil the infection was clearly more severe. The infected areas were 

 very 'large as were also the individual pustules. The most severely 

 attacked plants were in one pot which had been fertilized with manure 

 and bone meal. Aside from this one pot, however, there was but little 

 variation among the fertilized pots. The infection on the check plants 

 remained inferior, although it was very vigorous. 



Similar results were obtained from einkorn and lumillo plants. In 

 the case of these two forms the plants in the manure-and-bone series 

 developed the worst rust attack, the manure was next, and the plants 

 in ordinary soil were more lightly attacked. It should be remarked that 

 the differences- were not strikingly sharp, although they were quite 

 apparent. Emmer and Arnautka gave no distinct results. There was 

 a great deal of variation in the individual pots and no one series stood 

 out clearly from the other two. 



The Kubanka and Khapli plants showed some differences. The 

 character of infection is very different from that of the other forms. 



