POWDERY SCAB OF POTATOES. 3 



Pilz die Ursache der in Deutscliland "Schorr" genannten Krankheit ist, und viel- 

 leiclit audi der "Scab" der Englander, wiirde auch sonst die Verbreitung eine ganz 

 ansehnliche sein. 



Nevertheless he described it anew as Spongospora solani, and this 

 name was in general use until 1908, when Massee (1908 and 1910) 

 described it as Spongospora scabies, combining Brunchorst's generic 

 name and Berkeley's specific name, a combination which is re- 

 ferred to by Pethyb ridge (1913a) as not necessary and untenable. 

 Johnson, of Ireland, used the name applied by Brunchorst until 

 1909, when he found evidence to show that Brunchorst's Spongospora 

 solani was identical with Wallroth's Erysibe subterranea. In an 

 article published in 1911, Home is unable to confirm Johnson and 

 questions whether the organism described and figured by Wall- 

 roth, Martius, and Berkeley really is the same fungus described by 

 Brunchorst. In view of this fact he adheres to Brunchorst's Spon- 

 gospora solani. 



In a very recent article Pethybridge (1913a) brings forth still more 

 evidence to establish the identity of Wallroth's Erysibe subterranea 

 and the organism now known as Spongospora. He also emphasizes 

 the fact "that the question of identity does not rest merely upon the 

 degree of accuracy with which the spore balls are figured, but some 

 regard must also be paid to the very full description given by Wall- 

 roth of the development and fate of the warts, which agrees fully 

 with what we know of the behavior of Spongospora and which does 

 not apply to any other organism known at present." Judging from 

 the evidence now available as to the specific name of Spongospora, 

 it seems clear to the writer that it should be that first used by John- 

 son, namely, Spongospora subterranea (Wallr.) Johnson. 



DESCRIPTION OF THE DISEASE. 



This disease, so far as is known, never attacks the aboveground 

 portions of the potato plant. It is primarily a disease of the young 

 tubers, which develops as they mature in the ground. The earliest 

 stages of infection, according to Osborn (1911), "are visible on young 

 tubers not larger than hazelnuts. The disease is apparent by small 

 slightly raised pimples and a slight discoloration of the surface. 

 When cut open, the infected areas appear faintly purplish and 

 extend from approximately the outermost cells of the tuber toward 

 the deeper layers. Actual infection of the potato tuber by Spongo- 

 spora has not been seen, nor have infection experiments been success- 

 ful. The earliest stage in the fife history that has been observed is 

 that of a single uninucleate amoeba in a young potato cell near the 

 eye." Once in the tissues these naked masses of cytoplasm consume 

 the cell content and multiply rapidly, as shown in Plate I, A, and at 

 the same time stimulate the host cells to further growth and division. 



