118 rOTATO-FDNGUS, 



out, streamed all the protoplasm of the oospore, formed itself into a 

 ball, and then quickly divided itself, generally into from six to eight 

 portions (the number is variable), which, like so many zoospores, rapidly 

 quitted the dissolving gelatinous bladder (Fig 6, '). These zoospores 

 resembled those^of species of Peronospora and Pythium, and of Phyto- 

 phthora in form, structure, and movement (differing, perhaps, from the 

 latter to a small extent in size, but this was not precisely determined). 

 Like these they moved about a short time in the water, after which 

 they became quiet and gcrnainated. Their first tubes (germ-tubes) 

 remained short and without branching, even for several days, in the 

 cultivated specimens which have been described. In two hours after 

 sowing, the first zoospores were found, mostly in the drops of water. 

 Their number was usually much increased in ihe hours immediately 

 tollowing. 



Thus were developed young plants (germ-tubes) and zoospores 

 which completely resembled those of the Potato-fungus. Only one 

 thing was wanting ; but that was, without doubt, the chief thing, 

 viz., the proof that what was found really belonged to Phytophthora, 

 and not to some other Fungus resembling it and accompanying it. 

 The proof here required could only be obtained by ascertaining if the 

 young plants (germ- tubes) and zoospores would grow on a suitable 

 nidus or substratum into undoubted Phytophthora. There was no 

 need for uncertainty in determining this, since sufficient quantities of 

 the zoospores or germinating bodies of the oospores could be had, and 

 since the conditions attending the development of Phytophthora from 

 its spores were known. Accordingly I made numerous sowings of the 

 oospores in drops of water on fresh leaves, stalks, and tubers of the 

 Potato. The formation of the zoospores was easily confirmed in these 

 sowings. But nowhere did the young plants (germ-tubes) advance 

 beyond the stage of development which they reached on the glass, 

 nowhere did they penetrate into the interior of the living parts of the 

 plant, and nowhere did they dcvelope mycelium. This result, re- 

 peatedly confirmed with certainty, could mean nothing else than that 

 these oospores did not belong to Phytophthora, but to another Fungus, 

 which apparently had entered into the already dead tissues of the 

 tuber while it was still in the ground. The facts observed regarding 

 this Fungus corresponded best with the genus Pyihium ; and since it 

 did not take possession of the living Potato-plant, it was to be ex- 

 pected that, like most of the members of this genus, it would find its 

 suitable nidus or substratum in dead organic bodies. From experience 

 acquired in connection with other species of Pythium, 1 now made 

 sowings on dead animals, by placing small fragments — as the legs of 

 flies and newly-killed mites — on glasses, in drops of water in which 

 the zoospores of the Fungus were abundant. In this manner I might 

 be able to observe step by step the whole of the further development. 

 The zoospores at once attached themselves in great numbers to these 

 fragments, and sent out tubes which developed into splendid mycelium, 

 and ramified in the animal substances and in the surrounding water. 

 It did not form zoospores, but, on the other hand, it formed oospores 

 in the interior of the body of the mites, exactly like those found in 

 the cells of the Potato. I pass over here several other observations 

 which were made at this time, because they do not concern the 



