RiegHt AND Wrone Conceptions oF Puant 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 dicidium as recognized at the time were only stages in the life cycle 
of species of Puccinia and Uromyces, and other investigators soon followed 
with similar demonstrations for such genera as Roestelia, Peridermium, 
and Cawoma. It was in 1866 that he announced, with experimental proof, 
that one stage of a rust, as the cidium, often grows on a host wholly 
different from that on which the final stage grows, such rusts being called 
hetercecious. 
Hetereecism, 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 Wecidiuwm 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 
