WINTEKING OF THE UKEDO GENERATION". 47 



or sometimes on the ordinary autumn-sown crops even in the depths of winter. The 

 twisted leaves lying on the soil form a series of sheltered, moist chambers, on the 

 inner surface of which the rust pustules are occasionally present in great numbers. 

 These may develop with rapidity in the early spring, and at times as early as March 

 the whole of the plant's foliage may be yellow with rust. The winter's cold does 

 not appear to injure these spores, for they germinate readily when brought into the 

 laboratory, and there can be little doubt that they serve to start the epidemic in the 

 spring, when conditions become favorable for infection. Under these circumstances 

 it is not necessary to assume that the first appearance of any fungus in any season is 

 dependent upon its being actually present in the embryo of the grain, spreading 

 therefrom as the plant develops and ultimately producing its spores when the exter- 

 nal conditions are favorable. 



Australia. — McAlpine (74, p. 27) believed it probable that the red- 

 rust spores survive the winter in Australia and reproduce the fungus 

 again in the spring or summer. 



Cobb (36, p. 186) says: 



During the past two years it has been proved that the wheat rusts, that is, Puccinia 

 graminis and P. rubigo-vera, exist in the uredo stage all the year around in Australia. 



McAlpine (76, p. 20), from further observations on the wintering 

 of rusts in Australia, says : 



When the winter is mild and green vegetation flourishes, the mycelium of the 

 rust fungus may continue to grow and may even produce spores; whereas, if the 

 winter is severe and the mycelium does not remain in the perennial part of the plant, 

 then the continuance of the fungus is likely to be by teleutospores, which can last 

 through the winter on dead stems or other decaying vegetable matter. The so-called 

 wintering of the uredo depends so much on the climate that in a mild climate the 

 fungus may perpetuate itself exclusively by uredospores; whereas under severe 

 conditions it has to. resort to teleutospores. 



He further observes that in Australia it is the heat and drought of 

 summer which the rust must withstand, not the cold of winter, and 

 hence Puccinia graminis produces only comparatively few teleuto- 

 spores and lives over in the uredo stage in that country. During 

 the winter it is found in abundance on volunteer grains. 



The same author cites numerous instances of the germination of 

 the uredospore during winter. He says (76, p. 22): 



The uredo may become inured to unfavorable conditions, such as drought or cold, 

 and carry on the life of the species independent of the teleutospore. 



Such adaptation is seen in this country in Puccinia vexans Farl., 

 which, in addition to the ordinary uredo, has a specialized form, a 

 thick-walled, strongly papiUate amphispore. which germinates only 

 after a period of rest (31, pp. 22-25). 



United States. — Bolley in 1889 (21, pp. 13, 14) proved by a series 

 of observations that Puccinia rubigo-vera on wheat near Lafayette, 

 Ind., can pass the winter as " healthy fungal mycelium within the 

 tissues of the leaves,' 7 producing rust spores in abundance at the first 

 appearance of warm weather in March. "The very early appearance 



216 



