224 
Journal of Agricultural Research 
Vol. VII, No. 5 
abundant starch. The amebae finally bunch up around the host nucleus, 
which disappears before the spore ball is mature. The amebae vary from 
2.5 to 3 ju in diameter, are uninucleate and spherical, and contain a single 
nucleus, which stains heavily with safranin (PI. 8, fig. A). As in the case 
of the tuber, the diseased root cells differ from the healthy in that they 
show a large number of various-sized starch grains. 
In Solanum warscewiczii the infection is likewise confined to the 
phloem and the infected cells occur in groups (PI. 8, fig. B). These groups 
originate by continual division of one or more cells in both L. esculentum 
(PI. 8, fig. C) and 5 . warscewiczii (PI. 8, fig. B), which has been described 
by Nawaschin (10) for “clubroot” and called by him “ Krankheitsherde.” 
However, the starch grains are not as abundant nor as large in the cells 
of £. warscewiczii as in those of the potato or tomato; in fact, numerous 
infected cells without a trace of starch are often found. The host nucleus 
in the infected cells does not differ in size from those found in diseased 
cells, but the cells proper are increased in size and elongate and form the 
giant cells referred to by Kunkel (6) in the case of the potato. Such cells 
are also referred to in the case of Ostenfeldiella attacking Diplanthera 
wrightii . Two such giant cells from the potato partially surrounded by 
smaller healthy cells are shown in Plate 8, figure B. In one of these giant 
cells it will be noticed that there is only a single cross wall. In another 
case one of the cells after dividing into three cells showed early stages of 
another division. Each of the three cells measured approximately 22.3/z 
in diameter and was almost square, while the cells immediately surround¬ 
ing these and belonging to the same histological tissue measured only 
11.25/*. The amebae do not differ in size from those in the tomato, and 
as in the case of that host are found grouped around the nucleus. 
It will be noticed that spore balls were not produced on either the 
tomato or Solanum warscewiczii . This is due to the fact that the host 
plants had not reached maturity before they were killed by frost, the 
tomato being about 1 foot high and 5 . warscewiczii just blossoming. 
There can be no question, however, as to the causal agent in either case, 
as the amebae in both were uninucleate and showed the same measure¬ 
ments, staining reaction, position in the host cell, and presence in the 
phloem, which reacts alike in all of the different hosts. 
SPONGOSPORA SUBTERRANEA ON THE TUBER 
The first evidence of Spongospora infection on the tubers consists of 
faint, brownish purple, fimbricate, discolored areas about the size of pin¬ 
heads and resembling in outline very small bacterial colonies (PI. 10, 
fig. B). These spots indicate that the causal organism has entered and 
destroyed the cells immediately under the epidermal layer. At this stage 
the infection is comparatively superficial; but in from six to eight days the 
spot may increase in diameter to cm., lose its brownish color, and be 
replaced by a somewhat jellylike protuberance, consisting of metaplastic 
