HEREDITARY FACTORS AND GERMINATION 215 



accompanying the teliospores remained viable for a maximum 

 period of 59 days. 



Horner (1921) attempted to germinate the aeciospores of Puc- 

 cinia coronata avenue on leaves of Rhamnus kept in the herbarium 

 and found them non-viable 167 days after collection, whereas 

 urediniospores on Avena sativa, under the same conditions of stor- 

 age, were viable 87 days after collection. He also placed rust-in- 

 fected oat leaves in Petri dishes and stored them as follows: Five 

 collections were stored outdoors under a thick covering of leaves 

 and snow, at a temperature range of 27° to 42° F. Two of these 

 collections showed viable urediniospores after 44 days. Of four 

 collections placed unprotected outdoors, none showed viable 

 spores after 22 days. Both of the collections wrapped in paper 

 and stored in the dark at temperatures ranging from 29° to 86° F 

 had viable urediniospores after 79 days. Neither of two collec- 

 tions exposed to sunlight at 29° to 86° F had viable spores after 

 23 days. The urediniospores of this species kept outdoors in 

 Arkansas under the natural variations of temperatures and humid- 

 ity succumbed in 15 days [Rosen and Weetman (1940)]. Under 

 controlled conditions Rosen and Weetman found that spores were 

 short-lived at relative humidities below 25% or above 50%, irre- 

 spective of temperature. At higher temperatures and humidities 

 viability was lost in 15 days, and at lower temperatures and hu- 

 midities the spores survived for over 300 days. These results with 

 crown rust of oats and other similar ones with Puccinia graminis 

 triticij both heteroecious species, have an important bearing on the 

 problem of the source of inoculum in spring for infections on 



these cereals. 



Hart (1926) found a similar relationship between temperature 

 and humidity in the retention of viability of urediniospores of 

 Melampsora lint. They retained ability to germinate for almost 

 3 months at favorable temperature and humidity. At relative 

 humidities of 40% and 60% they were viable longer than at 20% 

 or 80%. When stored at high temperatures, they lost viability 

 more rapidly than when kept at low temperatures. 



Raeder and Bever (1931) recorded that urediniospores of Puc- 

 cinia glumarum, P. graminis phlei-pvatensis, and P. graminis tritici 

 remained germinable 88, 120, and 128 days, respectively, when 

 kept at a relative humidity of 49% and at a temperature range 

 between 9° and 13° C. At the same relative humidity and at 



