LIFE HISTORIES OF RUSTS. 13 



European forms the reader is referred to the works of Eriksson and 

 Henning, Klebahn, Ward, and others, cited later in this paper. 



RELATIONSHIPS BETWEEN AMERICAN AND EUROPEAN FORMS. 



Stem rust of wheat, rye, oats, and barley. — It has been known for more 

 than 40 years that the stem rust (Puccinia graminis Pers.) of wheat, 

 rye, oats, and barley in Europe may pass on to the barberry, produc- 

 ing secidia, the cluster-cup stage, on this plant. The same has been 

 likewise conclusively proved for the forms in this country. That the 

 stem rust always does pass through the barberry stage in each 

 season's sequence of forms, or that it can not live for more than one 

 season without passing on to the barberry, is not only not implied 

 but, as will be shown later, is absolutely disproved by field experience 

 and experiment. We know that rust can live for more than one 

 season without the intervention of the barberry, but we also know, 

 on the other hand, that the barberry stage is not uncommon in many 

 rust-infected districts, so that it may still be an important factor. 

 This feature will be further discussed. 



Leaf rust of wheat. — The aecidial stage of leaf rust (Puccinia rubigo- 

 vera tritici Carleton) of wheat is not known either in Europe or in this 

 country. Arthur (5) has shown that a similar rust on Elymus vir- 

 ginicus L. has a very common secidium on the jewel weed (Impatiens 

 fulva Nutt.). It can not be stated at present, therefore, whether this 

 rust has an secidium in this country, or whether it has entirely lost 

 this stage, as seems to be the case with Puccinia graminis in Australia. 

 It is a fact easily observed in almost any wheat area of the United 

 States, at least as far north as St. Paul, Minn., and Fargo, N. Dak., 

 that the uredo stage exists through the winter months in the severest 

 winters and the rust may thus live independent of an eecidial stage. 



Leaf (or crown) rust of oats. — In Europe the crown rust (Puccinia 

 coronata Corda.) of oats has its secidial stage on species of Rhamnus. 

 The exact identity of the European and American forms may perhaps 

 be open to doubt, though without question they are very closely re- 

 lated. It has been shown that in Europe two species of crown rust 

 exist (62), one (Puccinia coronata Corda.) with ascidia on Rhamnus 

 frangula L. and the other (Puccinia coronifera Kleb.) 1 with its secidia 

 on Rhamnus cathartica L. Neither of these secidial host species are 

 indigenous to this country, although they have been introduced and 

 grown quite extensively as ornamental shrubs in different localities. 

 The secidia of our own rust on oats is found on R. lanceolata Pursh., 



1 Eriksson on the basis of careful inoculation experiments has since separated the crown rusts into a 

 large number of physiological species, dividing Puccinia coronifera Kleb. with its aecidium on Rhamnus 

 cathartica into 8 physiological species and the Puccinia coronata (Corda.) Kleb. with its aecidium on Rhamnus 

 frangula into 3 physiological species (49). 



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