[ 12 ] 



II. 



CONSIDERATIONS AND EXPERIMENTS ON THE SUPPOSED 

 INFECTION OF THE POTATO CROP WITH THE BLIGHT 

 FUNGUS (PHYTOPHTHORA INFESTANS) BY MEANS OF 

 MYCELIUM DERIVED DIRECTLY FROM THE PLANTED 

 TUBERS. 



By GEORGE H. PETHYBRIDGE, B.Sc, Ph.D., 



Economic Botanist to the Department of Agriculture and Technical 

 Instruction for Ireland. 



[Read December 20, 1910. Ordered for Publication January 10. Published March 6, 1911.] 



It is now well over half a century since the potato bliglit became an 

 epidemic disease in Europe. During the latter half of this period the practice 

 of spraying tlie crop with some preparation of copper lias become more and 

 more prevalent aa a preventive measure against this disease, until at the 

 present time, in Ireland at least, spraying is generally regarded as an 

 essential item in the cultivation of the potato crop, experience having proved 

 its effectiveness and its necessity. 



During the same period, however, comparatively little attention has been 

 devoted to the extension of our knowledge of the fungus PhytophtJwm infestans 

 which causes the disease; and we are not yet in a position to say tliat its 

 life-history is completely known, although there are signs that tlie study of 

 it is once more being resumed in earnest. 



In one fundamental point, in particular, we are still almost completely in 

 the dark, and that is as to the manner in which the potato-plants first become 

 infected each succeeding season. 



We do know tliat, during the summer, "spores" are produced which 

 cause the spread of the disease from plant to plant during that season, but 

 whicli are ephemeral, and are incapable of living over the winter from one 

 season to the next. Judging from analogy, we should expect to find a second 

 form of spore, formed sexually, and provided with a thick wall, and thus 

 capable of living, probably in the soil, over the winter, and germinating in 

 the following summer. If, however, we except Worthington Smith's work (2)' 

 on this branch of the subject, which, although extremely suggestive, has not 



' Tlie numbers refer to the Bibliography at the end of the Paper. 



