232 Report of the Department of Botany of the 



PROBABLE LIFE HISTORY OF THE FUNGUS. 



Cronartium ribicola is an heteroecious rust fungus, parasitic on 

 Ribes and certain species of Pinus. In its aecial stage, which is 

 known as Peridermium strobi Kleb., it attacks the trunk and branches 

 of pine trees, producing a destructive disease called blister-rust. 

 The species of Pinus attacked are, exclusively, those which bear 

 their leaves in fascicles of five, the principal one being Pinus strobus, 

 the white pine. In its uredinial and telial stages the fungus occurs 

 on the leaves of various species of Ribes (currants and gooseberries), 

 both wild and cultivated. On these hosts it is known as felt-rust 

 and is of small economic importance. 



The fungus is perennial in the bark of pine trees, but the aecio- 

 spores, produced in spring, are unable to infect other pines. Hence, 

 the fungus cannot spread from pine to pine directly. It must first 

 go to Ribes and then back to pine. The infection of Ribes leaves 

 by aeciospores is followed, in from 10 to 21 days, by the appearance 

 of uredinia and, later, by telia. During the summer and autumn 

 the teliospores germinate in situ, producing promycelia which bear 

 sporidia and these are blown about by the wind and may infect 

 the pine host but not the Ribes. The urediniospores, on the other 

 hand, infect Ribes leaves readily so that the fungus spreads rapidly 

 from Ribes to Ribes during the summer and autumn; but since the 

 leaves are the only part of the Ribes plant affected and the uredinio- 

 spores are short lived, the career of the fungus on Ribes closes with 

 the falling of the leaves in autumn. That is, the fungus cannot over- 

 winter on Ribes. Such, in brief, is the life history of Cronartium 

 ribicola as it is generally understood. However, several European 

 mycologists have noted the occurrence of C. ribicola in localities where 

 the alternate host appeared to be lacking, and Eriksson, at least, 

 has expressed the opinion that it may live from year to year on 

 currants, entirely independent of the aecial stage on Pinus. 1 



PUZZLING OUTBREAKS AT GENEVA. 

 The first outbreak of the fungus in America occurred on the 

 Station gro unds at Geneva in the autumn of 1906. 2 It was quite 



1 Eriksson, Jakob. Einige Beobachtungen iiber den stammbewohenden Kiefern- 



blasenrost, seine Natur und Erscheinungsweise. Centbl. Bakt. [etc.] II., 2:377-394. 

 1896. 



2 Stewart, F. C. An outbreak of the European currant rust (Cronartium ribicola 



Dietr.) N. Y. (Geneva) Sta. Tech. Bui. 2. 1906. 



