230 



plaiuable by assuming that some urecliniospores or mycelium survived the 

 winter. 



It seems fair, then, to judge from the foregoing that a good many rusts 

 can pass the winter and propagate themselves for a long time, and probably 

 indefinitely, without the intervention of sexual reproduction. This is in 

 line with the experience of Freeman and Johnson, 40 who carried Puccinia 

 graminis, P. ruMgo-vera, and P. simplex through 52 uredinial generations 

 without apparent degeneration, and of Fromme. 41 who similarly carried P. 

 coronifera on oats through thirty-seven uredinial generations, and of car- 

 nation raisers generally, who still find the carnation rust an enemy to be 

 fought although it has in all probability never produced an a?cium on this 

 continent. 



The evidence, therefore, which is to be gained from the behavior of the 

 rusts concerning the question as to whether or not a plant species can long 

 maintain a high degree of vigor without sexual reproduction is quite 

 definitely in favor of the idea that it can. True it is that in the long cycled 

 rusts an effect of stimulation follows the stage in which the sexual fusions 

 take place, but this effect becomes dispelled by one or two uredinial genera- 

 tions, so that the rust is then back at the old level of vigor ; and it remains 

 there through an indefinite number of uredinial generations. 



Purdue University, 



Lafayette, Indiana. 



"Bur. Plant Ind. Bull. 216:34. 1911. 

 'Bull. Torrey Club 40:510-511. 1913. 



