Pethybridge and Murphy — On PhytophtJiora infestans. 569 



them with eold water. The filtered and sterilized extract, to which a small 

 quantity of beer- wort was added, proved itself an excellent medium, in which 

 copious mycelium was developed as well as conidiophores whicli were, as 

 regards size, but little behind those found on the potato plant itself. Brefeld 

 found no signs of oospores, and he says': — "In dem Pilz der KartofEelkrankheit, 

 Fhytophova infestans, liegt ein sicher erwiesener Fall vor, bei welchem Oosporen 

 nicht zur Ausbildung kommen und nur die Conidientrager auf der Oberflache 

 der befallenen, hier schnell absterbenden Pflanzenteile beobachtet werden 

 konnen. . . . Die Oosporen liessen sich bis jetzt in diesen Kultureu mit 

 Nahrlosungen auch nicht erzielen, wohl aber konnen wir nach der leichten 

 Ernahrung des Pilzes in Nahrlosungen mit allem Grunde annehmen, dass 

 der Pilz von seiner Uberwinterung in den Kartoffelknollen saprophytisch 

 in der Erde weiter wachst, iiber die Oberflache der Erde kommt und von 

 hier aus in seinen Conidientragern die Erzeugung der KartofEelkrankheit in 

 dem oberirdischen Krautig der Nahrpflanze, immer erst in vorgeriickter Zeit, 

 etwa im August, bewirkt." 



Meanwhile the question of pure cultures of the fungus in artificial 

 media had been taken up in the United States of America, and Clinton,^ in 

 1906, reported that he had obtained such cultures in vigorous condition on 

 plugs of living potato and on sterilized corn-meal and water, whilst less satisfac- 

 tory growths were developed on agar-media containing potato- and pumpkin- 

 juice respectively. In all some twenty-five to thirty media were experimented 

 with by Clinton ; but in no ease were any sexual organs discovered, although 

 in one instance some peculiar swollen bodies were observed which were 

 suggestive of immature oospores. Further results were published by Clinton' 

 in 1909, and, in particular, he found that the fungus grew readily and pro- 

 duced abundant eonidia on an agar- medium prepared from the juice of Lima 

 he3iMa{Phaseolus hinatm). In no case, however, were any sexual organs observed. 



Studies in the cultivation of the fungus had also been carried out by 

 Jones.'' In an abstract of a paper read before the the Botanical Society of 

 America, in December, 1908, some of the principal results are briefly stated. 

 The media employed were similar in character to those used by Matruchot 

 and Molliard, and by Clinton. In some of these media oogonia-like bodies 

 were obtained frequently ; in others, they were developed but sparingly. 



' Loc. cit., p. 116. 



2 Clinton, G. P. — Downy Mildew, or Blight, Phytophthora infestans (Mont.) de B., of Potatoes. 

 Eep. Conneotiout Agric. Exp. Station for 1905. 1906, p. 304. 



3 Clinton, G. P.— "Artificial Cultures of Phytophthora, with special reference to Oospores." Kep. 

 Conn. Agric. Exp. Sta., for 1907-8. 1909, p. 891. 



^ Jones, L. K., and N. J. Giddings.— Studies of the Potato Fungus, Phytophthora infestans. 

 Science, N. S., vol. xxix, 1909, p. 271. 



