Aug. i6, I920 Further Data on the Orange-Rusts of Rubus 511 



get much information on the question from the literature on the germi- 

 nation of rust spores. Most workers have not germinated aeciospores in 

 large numbers, and a few promycelia in their cultures might easily have 

 been overlooked. In order to settle this point it would be necessary to 

 germinate the aeciospores of many different rusts in large numbers, and 

 the writer has not undertaken this task. Nevertheless, it has seemed 

 desirable to make a thorough study of the aeciospore germination of 

 some other rust. For this study the aeciospores of Aecidium fraxini 

 were chosen. These aeciospores are produced in large numbers and 

 germinate readily on both water and Beyerinck agar. A. fraxini 

 was found in abundance on black ash trees growing along the shore of 

 Lake Champlain near Rouses Point, N. Y. Many cultures were made 

 with aeciospores of this rust. The germinations were carefully observed, 

 but not a single promycelium was ever found. Long, wavy germ tubes 

 were produced. No cross walls or branches were observed. These 

 spores produce germ tubes only. 



Promycelia in cultures of the aeciospores of Gymnoconia inter stitialis 

 indicate that the two nuclei which ordinarily pass out into the germ tube 

 and remain apart through many nuclear and cell divisions occasionally 

 fuse in the spore or perhaps in the young germ tube. If we assume that 

 reduction in chromosome number occurs here as in other promycelia and 

 that the sporidia produced are capable of reinfecting the host, then 

 G. inter stitialis has a double life cycle such as has not been demon- 

 strated for any other rust. 



It is not believed that promycelia are commonly produced even in small 

 numbers by the aeciospores of most rusts. On the other hand, it seems 

 probable that other rusts will be found that possess double life cycles. 

 Eriksson (j) has reported that the aecia of Aecidium graveolens which 

 occur on species of Berberis are able to reproduce themselves, although 

 they may also infect Avena elatior and give rise to Puccinia arrhenatheri. 

 This strange behavior, which has never been accounted for, may be due 

 to the production of promycelia by a certain number of the aeciospores. 

 Recently Klebahn (5) reports that the aecia of Periderinium pini repro- 

 duce themselves on the pine. He states that the aeciospores give germ 

 tubes, but a further study may show that some of them produce 

 promycelia. 



In an earlier paper (6) the writer expressed the opinion that the short- 

 cycled orange-rust is more primitive than the long-cycled one. The fact 

 that the long-cycled rust has a double life cycle is further evidence in 

 favor of this view. 



Arthur (j) considers the diflferences between the two orange-rusts 

 sufficient to place them in separate genera. Moreover, these genera are 

 widely separated in his classification. It would seem that the evidence 

 of a genetic relationship between these rusts should be given considera- 

 tion in any natural system of classification. 



