34 A STUDY IN CEREAL RUSTS 



that "lack of minerals in no way secured immunity from infection, 

 although seedlings deficient in phosphorus or nitrogen tended to show 

 retardation of infection." The well-nourished plants produced more 

 spores than the underfed ones. This seems to be due not so much to 

 the presence or absence of any particular chemicals and a direct effect 

 on the fungus but rather to the effect on the host. However, attempts 

 have been made to prevent diseases, among them rusts of cereals, by 

 adding various substances to the soil. Anderson (1890, p. 84) recom- 

 mends the use of salt, iron sulfate, and lime as tending to decrease the 

 amount of rust. Galloway (1893, p. 208) tried the effect of flowers of 

 sulfur, potassium sulfid, ammonium carbonate, potassium bichromate, 

 calcium hydroxid, and iron sulfate when applied to the soil, but found 

 them of no particular value in preventing rust. Laurent (1902, pp. 

 1040-1042) concludes that potatoes can be immunized against Phytoph- 

 thora infestans by treating the soil with copper sulfate. Marchal (1902, 

 pp. 1067 and 1068) tried the effect of copper sulfate and iron sul- 

 fate of various strengths when added to Sach's solution, on the se- 

 verity of attack of Bremia lactucae on lettuce. He found that by add- 

 ing 4 or 5 parts of copper sulfate to 10,000 parts of Sach's solution 

 he was able to render the plants practically resistant to the fungus, 

 yet leave the vegetation normal. In experiments attempting to immun- 

 ize cereals to rusts he was unsuccessful. Massee (1903, p. 142) pre- 

 vented the development of fungi on tomatoes and cucumbers by water- 

 ing them with copper sulfate solution. This did not give the desired 

 results with Oidium on barley. He states that not all plants can be 

 treated in this way without endangering their health. Chemical analy- 

 sis of treated % and untreated tomatoes showed that there was no more 

 copper sulfate in treated and therefore immune plants than there was 

 in those which had received no treatment. Massee suggests therefore 

 that the copper sulfate reacts with certain substances in the soil, thus 

 indirectly conferring immunity. Freeman and Johnson (1911, pp. 69- 

 70) call attention to the complexity of the problem and the need for 

 differentiating results. 



EFFECT OF WATER CONTENT OF SOIL 



Statements to the effect that low-lying, wet soils predispose cereals 

 to rust are frequently made in the literature of the subject. Reference 

 has already been made to some of these. It was observed very fre- 

 quently in experiments mentioned in this paper that when the relative 

 humidity was high infection was not only surer to result but that it 

 was also more severe. It was therefore thought worth while to de- 

 termine whether a high water content of the soil would act as a pre- 

 disposing factor. 



The varieties used were: Einkorn 2433, Kubanka 1516, lumillo 



