OBSERVATfONS ON THE GENUS PYTHIUM. 495 



species may he largely extended. I have cultivated this 

 Pythium successfully on the young buds of Carrot, on cut 

 slices of Potato and Dalilia tubes, and on the stems of ordinary 

 greenhouse Pelargoniums. 



T do not here propose to go very fully into the details of 

 these cultivations, since it seems probable that prolonged 

 research will yield facts of more general significance than may 

 be safely stated at present. The following observations, how- 

 ever, are true so far. The mycelium of the Pythium confines 

 its ravages to the parenchyma cells of the seedlings, stems, 

 and tubers, and, so far as I could discover, never enters or 

 crosses a fibro-vascular bundle; in well developed specimens, 

 however, vigorous branches envelop the vascular bundles, and 

 possibly obtain nourishment from the young sieve tubes. The 

 conidia and sexual organs become formed in any invaded 

 parts of the parenchyma, as well as on the exira-matrical 

 branches of the mycelium. The mode of action of the myce- 

 lium seems to be always the same. It consists, speakint' 

 generally, in the absorption of the dissolved materials of the 

 cell contents, leaving behind a series of empty bags enveloped 

 — e.g. in the case of a cress-seedling — by the common cuticle ; 

 these remnants become more gradually the prey of Bacteria 

 and saprophytes. 



Although the above statement is true so far as it goes, there 

 are some details of importance in the modus operandi of the 

 parasite, which I can only touch upon here, since I hope 

 to obtain more information during the course of experiments 

 now in progress. 



In cultivating this mycelium on slices of Potato and Dahlia 

 tubers, for instance, I noticed particularly that the starch 

 granules of the former, and the inulin of the latter are not 

 directly attacked by the mycelium. This is very clear in the 

 case of the Potato; the starch grains remain intact long after 

 the hyphse have destroyed all other cell contents. In the 

 Dahlia, the difficulty consists in deciding whether the inulin 

 sphere-crystals (precipitated by alcohol in the usual manner) 

 have diminished in the invaded cells ; I think that such is not 



