MICHIGAN ACADEMY OF SCIENCE. 189 



the pines, he foniid the Sweet Fein rusted to a distance of about 

 forty yards. On the soutli the rusted area extended about in yards. 

 He also found that along- the i)ath which the workmen took from 

 the pine plantation to the nursery, the Sweet Fern bordering this 

 l>ath had considerable rust. 



The pustules on the Sweet Fern first contain only uredospores, 

 but later masses of toleutospores form a column arisinc; from the 

 old uredosporic sori. This is characteristic of the genus Cronartium. 



The teleutospores are carried from the Sweet Fern to the pine 

 seedlings which thev then infect. In this case the infection is not 

 observable till after the first two to three years. The mycelium is 

 growing slowly under the bark of the pines and the hypertrophy 

 and decidia. which are the means of recognizing the disease, do not 

 show for the first few years. As soon as aecidiospores are produced 

 by the ]>eriderium stage on the pine, they infect the Sweet Fern 

 during siiring or early summer and here development is rapid and 

 crops of uredospores and teleutospores are soon produced.. 



The authorities at Koscommon were strongly advised to thorough- 

 ly burn over and destroy' the portioii of laud occupied by the in- 

 fected Pine, as well as the area of Sweet Fern surrounding the tract 

 at least as far as the spores were shown to have been carried by the 

 wind. This is reported to have been done. The complete annihila- 

 tion of the rust or sterilization of the region by this method can 

 however scarcely be considered perfect and a sharp lookout will 

 have to be kept in the future. The eradication of either host if this 

 were fciisible. is of course the most desirable. 



The question naturally arises how did the rust get a foot-hold. 

 The Western and Lodgepole Pine seedlings were raised fi*om seeds 

 sowTi in 190G. hence there is only a slight chance that the seeds 

 carried teleutospores of the Sweet Fern. Infection appears to have 

 occurred later, as the first sign of the disease appeared in 1911. 

 Mr. ^Vlains examined the native pines within reach, but found no 

 rust. It is possible that the nist is harbored by the Jack Pine or 

 one of the other native pines. It seems to me much more likely 

 that some stray spores were brought in on one of the many articles 

 which a civilized community nowadays imports for its use. 



