334 Osborn . — Spongospora subterranea , ( Wallroth ) Johnson . 
may be taken as an average size. The ‘ spore balls ’ are marked by numerous 
depressions and fissures (PI. XXVII, Fig. 16), as has been described, arising 
from the formation of clefts in the plasmodium. Harper has described 
minutely the progressive development of the cleavages that characterize the 
development of the spores in Fiiligo . The whole plasmodium is so small in 
Spongospora that no such full description can be given, but since cleavages 
are to be noticed in the plasmodium at any time after its formation (Figs. 7 
and 10), though not generally till the time of the second mitosis (Fig. 14), 
it is obvious that in Spongospora , as in the Mycetozoa, the segmentation of 
the protoplasm is independent to a great extent of nuclear division. 
The spore in all cases that I have observed is uninucleate, the nucleus 
having a karyosome and other chromatin matter. 
Unfortunately all my cultures of the spore balls have proved intract- 
able, so that I have not been able to observe the germination of the spores. 
Professor Johnson has not seen this either, Massee’s account 1 being the only 
one published. He records that the contents of the spores escape intact, 4 and 
are irregularly globose in form, with a few small projections. They show 
a very sluggish movement for some time, after which they become stationary. 
The diameter of the amoeboid body after its escape from the cell is about 3 \xb 
Effect upon the host pla 7 it. The effect of Spongospora upon its host has 
to some extent been described already. Under dry conditions of the soil the 
external appearance is limited to small circular patches about 5 mm. across. 
Under wet conditions the damage is more serious, and the scabs may be as 
large as 3-4 cm. in diameter and as much as 2 cm. in depth. This is the 
only external appearance ; there is no sign of hypertrophy nor any distor- 
tion other than that caused by the pitting. 
A definite cork cambium is formed below the seat of injury, though 
amoebae are to be observed in the deeper layers of the tuber under the cork. 
In the host cells it is apparently the starch that is especially attacked, 
and starch grains 'of any size are generally absent at the time of spore 
formation. This is certainly not so in the initial stages, nor even up to 
the time of plasmodium formation. It is, of course, possible that starch 
does not develop in those cells that are attacked when young, the soluble 
carbo-hydrate material being absorbed as it enters the cell by the parasite. 
The subject, however, needs further investigation, which it is hoped to 
carry out. 
About the time that the plasmodium is formed, the host cell appears 
to be exhausted, and most of its cytoplasm has disappeared. This is not 
the case with the nucleus, which has become much enlarged and unhealthy 
in appearance as the attack has proceeded. Many of the nuclei show remark- 
able lobing and indentations (Figs. 5 and 12), and they are often closely 
applied to the plasmodium of the invader (Figs. 7 and 12). The nuclei 
1 Massee, G. : loc. cit., p. 598. 
