Methods in Eust Investigations 243 



minable condition in the spring when their alternate hosts are in the 

 best condition for infection. 



2. Germinability of Spores. In general, aeciospores and uredinio- 

 spores are capable of germinating when they naturally become detached 

 from the spore chain or pedicel, spores not germinating being considered 

 either immature or too old. A number of the rusts under investigation 

 in this laboratory, however, have given only fair to moderate germina- 

 tion of urediniospores under conditions which indicate other factors of 

 importance. Urediniospores of Puccinia Sorghi and Pucciniu triticina, 

 collected from greenhouse material on Jan. 26 and Feb. 1, 1921, and 

 stored out of doors in vials, shov/ed an increase in germination when 

 tested Feb. 11 and March 1. We have found that drying for several 

 days greatly increases germination of such spores. Melhus and Dur- 

 rell (1919) have noted a similar condition for the urediniospores of 

 Puccinia coronata. They found that storage of these spores in vials 

 resulted in a marked increase in germination, indicating a maturation 

 of the spores, even after detachment from the pedicel. It is very likely 

 that the conditions under which these spores are formed have an impor- 

 tant bearing upon their viability. But little seems to be known con- 

 cerning this question. 



On the other hand, the factors bringing about germinability in 

 teliospores have received more attention. This probably is due to the 

 fact that the teliospores of many species function as re.sting spores and 

 usually are germinable only after weathering, generally over winter. 

 This has stimulated investigation as to the factors concerned. Klebahn 

 (1914), Maneval (1922), and the writer (1916) have shown that the 

 teliospores of such species may be brought into a condition for germina- 

 tion by alternate wetting and drying or by more or less prolonged soak- 

 ing without exposure to winter conditions. Thiel and Weiss (1920) 

 have been able to bring about a condition for germination by treatment 

 of teliospores of Puccinia graminis with citric acid. These methods may 

 be found helpful in some investigations, as teliospores made germinable 

 in the fall or early winter enable work to be carried on at a time of 

 year when greenhouse conditions are more easily controlled. However, 

 if the alternate host is a perennial, complications are introduced, as it 

 will be necessary to bring it out of its resting period and into a vigorous 

 growing condition. 



That, even in nature, conditions sometimes may occur which bring 

 about a considerable deviation from the typical situation, was noted in 

 1920. Thus two collections of Puccinia monta^iensis Ellis, two of P. 

 Koeleriae Arth., five of P. Clematidis (DC.) Lagerh., eight of P. procera 

 Dietel and Holw., three of P. apoc7-ijpta Ellis and Tracy, and fourteen 

 of P. triticina showed teliospores germinating vigorously when brought 

 into the greenhouse on Dec. 10 and tested. Collections of teliospores of 

 these species tested the two previous seasons during the fall gave no 

 germination and it has been generally considered that the teliospores of 

 these species are germinable only after overwintering. All of the above 

 collections were placed outside again and overwintered, and seventeen 

 of them were still germinable when tested during March. On the other 



