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Right and Wrong Conceptions of Plant Rusts. 



By J. C. Arthur. 



The plant rusts have been known both popularly and scientifically 

 from the earliest times. Their study took the usual course of development 

 of all cryptogamic plants up to the time that DeBary demonstrated that 

 pleomorphism existed in many species in a more striking manner than 

 known in other fungi. He showed that most if not all members of the 

 genus Mcidium as recognized at the time were only stages in the life cycle 

 of species of Puccinia and Vromyces, and other investigators soon followed 

 with similar demonstrations for such genera as Roestelia, Peridermium, 

 and Gccoma. It was in 1866 that he announced, with experimental proof, 

 that one stage of a rust, as the /Ecidium, often grows on a host wholly 

 different from that on which the final stage grows, such rusts being called 

 heteroecious. 



Heteroecism, which was thus established by DeBary and confirmed 

 by his contemporaries, was not generally accepted by mycologists for a 

 score or more of years. That the /Ecidium poculiforme of the barberry 

 leaf, with its conspicuous cups filled with chains of verrucose spores, could 

 not give rise to other similar cups on the barberry, but only to the pow- 

 dery and echinulate spores of the red rust on wheat stems, as unlike the 

 former as a caterpillar is unlike the pupa into which it is transformed, 

 was such a strikingly new idea in botany, that when once it did find gen- 

 eral credence, and was extended to many other species by culture work, 

 it assumed undue prominence. This result was accelerated by the rather 

 recent discovery of races, or so-called physiological species. When the 

 well known Puccinia graminis, which has great economic importance by 

 producing a destructive disease of cereals and grasses, became also one 

 of the best illustrations of the division of a species into physiological 

 strains or races, more or less well established, in some cases amount- 

 ing to possible species, it assumed in the minds of many mycologists a 

 typical position in reference to other rusts. It became common to speak 

 of rusts as agreeing with Puccinia, graminis in their life cycles and spore 

 structures, or in showing a certain amount of deviation from it. This 

 attitude has caused considerable distortion in the conception usually held 



