C02 Journal of Agricultural Research voi. xix, no. lo 



dewberry plants, so far as has been observed, is short-cycled in this 

 region. Wild blackberry and black raspberry plants occur abundantly 

 along the Potomac River in both Maryland and Virginia. They are 

 frequently intermingled with each other, and often both are infected 

 with orange-rust. During the springs of 191 7 and 191 8 the two rusts 

 were many times found growing close to each other, and during both 

 seasons the telia of Gymnoconia were found occurring sparingly on leaves 

 of wild black raspberry plants. The telia were always found on or near 

 those plants that had borne caeomas of Gymnoconia. They were never 

 found on any blackberry host. Many cultivated blackberry and black 

 raspberry fields in the vicinity of Washington are troubled with orange- 

 rust. In every instance the germination tests have shown that the 

 raspberry plants are infected with the long-cycled rust. Rust found in 

 the cultivated blackberry fields is always the short-cycled form. 



Plate 92 shows the way the aeciospores of the two rusts germinate 

 on Beyerinck agar at room temperature (about 25° C). The spores 

 shown in Plate 92, A, were taken from leaves of wild black raspberry 

 at West Falls Church, Va. They have produced long germ tubes. 

 Those shown in Plate 92, B, were collected at the same place on wild 

 blackberry. They have produced promycelia-bearing sporidia. 



INFLUENCE OF TEMPERATURE ON GERMINATION 



In order to study the effect of temperature on germination numerous 

 collections were made from both wild and cultivated blackberry and 

 raspberry plants. The spores were germinated in Petri dishes on water 

 and on Beyerinck agar. The cultures were incubated at temperatures 

 varying by 5° intervals and ranging from 0° to 30° C. None of the 

 spores of either rust germinated at 0°. At 5° excellent germination 

 was obtained, but growth was slow. At all of the higher temperatures — 

 10°, 15°, 20°, 25°, and 30° — the spores of the two rusts germinated 

 equally well. It was noted that at low temperatures such as 5° and 

 10° the spores of the long-cycled rust began to germinate somewhat 

 sooner than those of the short-cycled rust. Germination in cultures of 

 both kinds of spores took place more rapidly at 30° than at any of the 

 lower temperatures. Fewer spores germinated, however, at this tem- 

 perature than at the lower temperatures. The spores of both rusts 

 germinated well at all the temperatures tested between 0° and 30°. 



Spores taken from blackberry leaves always produced promycelia, 

 while those from the black raspberry leaves produced long germ tubes. 

 Mature aeciospores of the two rusts collected at the same time and 

 often within a few feet of each other and incubated at the same tem- 

 peratures and on the same media always showed the same differences in 

 manner of germination. The promycelia produced by the spores from 

 blackberry leaves are typical in every way. They become divided into 



