jtineis, I9IS Spongospora Subterranea 277 



to be the case. When portions of encysted plasmodia are transferred to 

 fresh agar, the cysts germinate and give rise to a large number of amoebae, 

 which form pseudoplasmodia and fruiting bodies Hke those above 



described. 



SUMMARY 



(i) So far as known, the type of infection here described has never 

 before been observed. Infection of growing potato tubers by Spongo- 

 spora subterranea is accompHshed not by separate amoebae, as has pre- 

 viously been supposed, but through the action of a plasmodium which 

 invades the tissue and infects a large number of cells at each point where 

 it enters. The conception of a plasmodium invading healthy tissue, 

 pushing down between the cells, and finally infecting them, is, it would 

 seem, new to pathology. S. subterranea actually lives within the proto- 

 plasm of its host. In this respect it differs from most fungi and bac- 

 teria and offers an especially favorable opportunity for the study of the 

 relations of host and parasite. 



This account of the life history of 5. subterranea raises many interesting 

 questions regarding other members of the Plasmodiophoraceae. The 

 manner in which infection takes place is unclear in the life history of all 

 the members of this group. Do the amoebae of Plasmodiophora brass icae 

 produce plasmodia outside of the living cabbage cells ? Are the cabbage 

 cells attached by uninucleate amoebae as was supposed by Woronin (17), 

 or do they become infected in a manner similar to that above described 

 for potato cells attacked by 5. subterranea? The distribution of the 

 diseased tissue in the roots of the cabbage suggests the latter method of 

 infection. 



(2) The cells in each little island of infected tissue are stimulated to 

 abnormal growth and division. 



(3) While the tubers are in storage the spores germinate in the base 

 of the old sori and produce amoebae which come together to form plas- 

 modia that cause secondary infections. 



(4) These plasmodia feed on the tissue around the old sori and cause 

 a so-called dry rot, which is probably a mild form of the canker stage of 

 the disease. 



(5) The spores of 5. subterranea germinate in culture media and each 

 produces a single uninucleate amoeba. 



(6) When conditions become unfavorable the amoebae encyst and go 

 into a resting stage. 



(7) The amoebae seem to produce saprophytic plasmodia on culture 

 media. 



