242 Report of the Department of Botany of the 



currant rust which has appeared at Geneva. They were cut down 

 and burned on May 17. 



About 120 feet south of the affected pine trees there was a small 

 currant plantation containing both red and black currants. It was 

 thought that the fungus might not have had a chance to infect these 

 currants. For several days prior to May 15 the weather was dry 

 and unfavorable for infection. The forenoon of May 15 was damp, 

 but in the afternoon it dried off and remained dry until after the 

 trees were destroyed. Thus it appears that the forenoon of May 15 

 was the only time when there was a chance for the currants to become 

 infected. Nevertheless, infection occurred. A considerable number 

 of uredinia were observed on June 10. Although both red and black 

 currants in this plantation became quite abundantly infested with 

 felt-rust and none were destroyed until about September 10, at 

 which time the black currants were dug out and burned, the fungus 

 did not spread to other currant plantations in the vicinity. Its 

 failure to spread was due, probably, to the dry weather prevailing 

 during the greater part of the summer and autumn. 



DISCUSSION OF RESULTS. 



The writers agree with Drs. Arthur and Spaulding that the results 

 of these experiments do not prove conclusively that Cronartium 

 ribicola never over-winters on Ribes. Negative results in experi- 

 ments of this kind are never conclusive. Our interpretation of the 

 results is that such over-wintering occurs rarely, if at all, and only 

 under very exceptional conditions. The chances of over-wintering 

 are so small that it is unnecessary to quarantine currants affected 

 with felt-rust. The only precaution which needs to be taken is 

 that affected plants are not shipped until after the leaves have 

 fallen. 



It may be argued that teliospores carried on or with affected 

 currant plants may become a source of infection for pine trees; and 

 because of this danger the distribution of affected currants should 

 not be permitted. The writers consider that this objection is suffi- 

 ciently answered by pointing out that the countless multitudes of 

 teliospores which have been produced in the vicinity of Geneva 

 during the past seven years have not infected a single pine tree so 

 far as can be determined. However, if it seems that additional 

 evidence is required it may be said that, normally, the teliospores 



