324 



THE BASIDIOMYCETES 



barberry is absent, and with P. coronata in Andean regions of 

 South America, where Rhamnus is absent. Such rusts may sur- 

 vive the winter by migration in the autumn from colder to 

 warmer portions of the country, multiplying there during win- 

 ter, and again migrating to colder regions in the spring. Stakman 

 and his associates have amassed abundant evidence to show that 



Fig. 124. Urediniospores of various rusts, in surface view and in optical 

 section. (Adapted from Arthur.) A. Uredinopsis mirabilis. B. Milesla 

 polypodophila. C. Cronarthmi ribicola. D. Coleosporhnn solidaginis. 

 E. Melcmipsora abietis-canadensis. F. Physopella fici. G. Pileolaria toxi- 

 codendri. H. Fiiccinia grmninis. I. Tranzschelici pnmi-spinosae. J. Kuebne- 



ola uredinis. 



there is a seasonal migration of P. graminis of this kind in the 

 Great Plains area of the United States. There is also abundant 

 evidence that this rust and other orrain rusts cannot survive the 

 winter as urediniospores in the Northern United States or in 

 northern Europe. In Australia viable urediniospores of P. gravii- 

 72ts, P. trkicinay and P. chry santhemi have been taken from sori at 

 various times during the winter by McAlpine. 



Certain autoecious species also persist and perpetuate them- 

 selves in the uredinial stage. Such is reported to be the situation 

 with Uromyces fabae in Ecuador, whereas this same species in 

 Europe produces aecia and also telia. Plasticity among rusts may 

 find expression in other ways, such as the occurrence of short- 

 cycled forms like Kiinkelia nitens and Fiiccinia podophyUi. 



