1892.] PUBLIC DOCUMENT — No. 33. 229 



shaken. Later the leaves of summer wheat on adjoining 

 plots were very badly affected. In July this stage of the 

 fungus had largely disappeared, and the leaves of the rye 

 were blackened by the winter-spore pustules of the same 

 fungus. 



The life-histories of this and the related species of rusts 

 are not yet fully understood, and our only protection at 

 present is in destroying as completely as possible the stubble 

 and all refuse which can harbor their spores in the field. 

 Observations by the writer, made as his share in certain 

 co-operative studies of the grain rusts, seem to indicate that 

 this rust does not survive the winter in its host-plant, but 

 depends upon fresh infection in the spring. On our plots 

 the summer-spore pustules on rye seedlings survived the 

 early frosts, and seemed vigorous until the heavy frosts and 

 first snowfalls. The plots were then covered continuously 

 by snow until spring. When they were again exposed, the 

 discolored spots where the spore-pustules had been could be 

 readily observed, and examination showed a mycelium to be 

 present in the spot. But it was apparently dead, for 

 repeated examination of the plots failed to detect new spores 

 breaking out from any of these old spots. The fungus was 

 not observed after growth was resumed until early in June, 

 when a few warm and moist days increased the amount 

 present from a few scattered spots to a general epidemic. 



The virulence of this attack of rust caused a marked weak- 

 ening of the plants, as was shown by the yellow color of 

 their leaves and by the abundant presence upon the leaves 

 — most abundant on the weakest ones — of the saprophytic 

 fungus form known as Cladosporium herbarum (Pers.) Lk. 

 The sooty patches of this with the orange masses of the rust 

 pretty completely covered the leaves and left little or no 

 normal tissue. 



It is noteworthy, as illustrating the general principle 

 repeatedly laid down in these reports, that on those plots 

 which had been supplied with abundant and readily available 

 nitrogen the effects of the fungi were much less serious than 

 where the supply of nitrogen was deficient in quantity or in 

 availability. The difference was especially striking in re- 

 spect to the discoloration of the leaves, which was less in 



