Pethybeidge — On the Rotting of Potato Tubers. 551 



the soil, it could extend from that source, and that upon the out-growths 

 oospores would be developed, which of course would render the soil capable of 

 causing the infection of a fresh crop through the subsequent germination 

 of these spores. It seems also not unreasonable to suppose that if the soil 

 contained an excessive amount of moisture the production of couidia as well 

 as of oospores would result. Whether, however, it is possible for this 

 development of oospores or couidia to take place in the soil from the surface 

 of an unwouuded but affected tuber must for the present be regarded as 

 doubtful, although it seems almost certain that by some means the soil in 

 which affected plants have been grown does become contaminated with the 

 fungus. 



VI. Affinities of the Fungus. 



The genus Phytophthora was founded by de Bary in 1876, and in it 

 was placed in the first instance the potato-blight fungus, then known as 

 Peronospora iitfestans. Subsequently other species of Perouospora, which 

 agreed with P. infestans in the mode of development of their conidia, were 

 transferred to the new genus. 



The species of Phytophthora enumerated in Saccardo's great work 

 " Sylloge Fungorum," are as follows : — 



(1). Phyiophiliora infedans de Bary. 



(2). P. Cadorum Sohroet. (Synonymous with Peronospora Cadornm 



Lebert and Cohn ; Per. Fagi Hartig ; Per. Senipervivi Schenk, and 



Phytophthora omnivora de Bary.) 

 (3). P. Phaseoli Thaxter. 

 (4). P. Colocasiae Raciborski. 



To these species must be added the following : — 

 (5). P. Nicotianae van Breda de Haan (11). 

 (6). P. Thalictri Wilson and Davis.^ 

 (7). P. ^yr%ffe Klebahn (16). 



(8). P. Faberi Maublanc,- possibly synonj'mous with 

 (9). P. Theobromae Coleman (7). 

 (10). P. omnivora var. Arecae Coleman (7). 

 (11). P. agaves [? Gandara] (10). 

 (12). P. Jatrophae Jensen. 



The last-named but one of these species is known to me by name only 

 from a reference in Hollrung's Jahresbericht,^ and a culture of the last- 



1 Bull. Torrey Bot. Club, vol. xxxiv., 1907, p. 392. 



^ L'Agric, Prat., d. Pays Chaiids., No. 79, 1909, p. 315. 



= Band xiii., 1912, p. 347. 



