POWDERY SCAB OF POTATOES. 5 
Pilz die Ursache der in Deutschland "Schorf " genannten Krankheit ist, iind viel- 
leicht auch der "Scab" der England er, wiirde auch sonst die Verbreitung eine ganz 
anselmliche 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 Briinchorst'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 Waliroth'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, Martins, and Berkeley really is the same fungus described hj 
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 Waliroth'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 ceils 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 life 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. 
