226 
Journal of Agricultural Research 
Vol. VII, No. s 
The symptoms are not fully comparable with those produced in the 
greenhouse, although they had some points in common, as is shown in 
Plate 10, figures C, D, and E. The diseased surface of this material pre¬ 
sented the appearance of having been gnawed and chewed by insects 
after S. subterranea had made its appearance. The wide variation in the 
symptoms of this disease emphasizes its dependence on environmental 
conditions. 
The resemblance of the injury caused by the flea beetle to that caused 
by the sori of Spongospora subterranea is very striking, as evidenced by 
the fact that specimens showing the former were received from several 
pathologists with an inquiry in each case as to whether the injury was due 
to powdery-scab. There is no doubt that insects play a r 61 e in the de¬ 
struction of the diseased portions of the potato plant. The injury prob¬ 
ably caused by the flea beetle and other subterraneous larvae (PI. io, fig. 
A) can be distinguished from that due to 5 . subterranea by the fact that 
in its earlier stages there is a minute central opening caused by the punc¬ 
ture of the insect, and in its later stages the affected area may show defi¬ 
nite splitting, which, however, does not extend very deep into the tissues. 
Frequently the central portion of the raised area is crumbled, and it is at 
this stage that the trouble is most often confused with the open pustules 
of 5 . subterranea . At this stage also it shows another similarity to 5 . 
subterranea —that is, the sunken area immediately surrounding the sorus, 
which is due either to what is designated and described later in this paper 
as physical drying out (Pl. n, fig. F, H) or to the action of the plasmo- 
dium (PI. n, fig. D). 
In. the course of the work the writers also received many specimens 
showing enlarged lenticels (PI. io, fig. F), resembling superficially the 
early stages of powdery-scab, with an inquiry in each case as to whether 
the injury was due to Spongospora subterranea. Intumescence associated 
with the lenticels develops when the tubers are held in moist chambers 
for io days. The proliferation of the cells below and around the lenticels 
at the end of that time resembles the protruding hyperplastic tissue of 
the sorus in early stages of formation. A microscopic examination and 
the identification of spore balls within the sorus, however, is the cri¬ 
terion for determining the disease, but, as will be pointed out in the 
following paragraphs, care should be taken not to confuse the spore form 
of other fungi with the spore balls of S. subterranea. 
CONFUSION IN EARLIER WRITINGS DUE TO THE FUNGI ASSOCIATED 
WITH SPONGOSPORA SUBTERRANEA ON THE POTATO TUBER 
Wallroth (15) and Berkeley (1) described fungi associated with a 
potato disease which bear a striking resemblance to the spore balls of 
Spongospora subterranea , and earlier investigators observed numerous 
fungus threads in the sori, all of which resulted in much confusion and 
error. The writers believe that the “bulbils” of a species of Papulospora 
