496 H. MARSHALL WARD. 



the case. Long after the cells had become traversed by the 

 hyphae, I was able to obtain sphere-crystals of inulin in quan- 

 tities which seemed to me not less than in cells which were 

 still uninjured. 



Again, in the stems of pelargoniums cut in November, 

 and into which the Pythium was allowed to grow, the starch 

 granules could be recognised even after the Pythium had 

 formed its conidia and oogonia. 



It seems highly probable from these observations that P y- 

 thium De Baryanum — not to extend the generalization too 

 far at present — is unable to dissolve starch grains unaided; on 

 the other hand, it is quite certain that it absorbs material from 

 the cell contents. 



My observations so far have led to the following conclusion 

 as to the mode and sequence of action of this parasite on the 

 cells of the Potato and Dahlia tubers. Certain portions of 

 the protoplasm and cell sap are directly attacked, and absorbed 

 immediately, but of course we cannot say unchanged. The 

 hypha grows at the expense of these, enters another cell, and 

 leaves the starch-grains, part of the protoplasm, and the 

 nucleus untouched. 



During these processes the walls of the attacked cells turn 

 brown, especially where the hyphal tube entered the cell, and the 

 dead granular remains of the protoplasm and nucleus soon 

 acquire a similar yellow-brown colour. Starch grains may 

 often be observed embedded as in a matrix of these yellow- 

 brown granular remnants, and, if detached from it, one notices the 

 cavity from which the starch grain has fallen as from a mould. 

 I have observed a similar phenomenon in potatoes invaded by 

 Phytophthora infestans, and Prof. De Bary had noticed it 

 in this case also. It is well known that this Pythium grows 

 better in very young cress-seedlings than in those more 

 advanced, and this seems to be in accordance with what is 

 stated above ; unless it is assumed that the more developed 

 cell-wall of the advanced seedlings simply prove formidable 

 barriers to the progress of the hyphse, a supposition which does 

 not seem to cover all the facts. 



