Ill rOTATO-FfNGUS. 



such tubers and place them in a moist atmosphere, tlie Fiin':ius grows 

 luxuriantly from the out surface, and forms stronger couidiophores 

 than anywhere else. In a moist atmosplicre the Fungus will send out 

 oonidiophorps through the skin ; and Kiihn* has callo(l attention to tho 

 fact that this phenomenon occurs in cellars without artificial en- 

 couragement. Since then known facts do not exclude tlic possibility 

 of l^hytophthora being a Saprolcgyiia, or, at any rate, being closely 

 allied to Saprolegniece, and since most Fungi of tliis family grow in 

 water, ■while even the few species which are parasitic on land plants 

 fructify most abundantly under water, the question arises whether 

 this may not also hold good of the Potato-fungus, parti^^ularly as re- 

 gards tlie formation of oospores. Accordingly, tubers with abundance 

 of mycelium were repeatedly placed in spring- water. The invariable 

 result was that numerous branches from tlie mycelium grew in the 

 water. These had the same peculiarities as bran(dies sent out in the 

 moist air ; some even assumed the character of couidiophores, forming 

 at the extremity conidia, which, without falling otf, produced zoo- 

 spores, resembling in this respect the sporangium of Saprolegniece. 

 But each time this entire water-vegetation of the Phgtophfhora quickly 

 perished with the corruption of the Potato, and not the slightest trace 

 of oogonia was found. The same experiment was repeatedly made 

 with stalks and leaves which were filled with the Fungus, but always 

 without any positive result, because a plant wliich the Fungus has 

 attacked at once becomes rotten in water, and the FInjtophthara 

 dies as soon as the surrounding tissues are rotten. 



The experiment was then so far changed by placing tho same sub- 

 stances in moist earth instead of in water. From the tubers grew up 

 the usual conidiophores ; but here also the stems and leaves quickly 

 became rotten, and the Fungus with its oogonia nowhere occurred. 

 Other forms of Fungi, not belonging to Phytophthora, were, it need 

 not be said, very often found. 



5. After these successive failures, there still remained a possible 

 method of discovering the oospores, suggested by another phenomenon 

 observed in the tubers. It is known that Potatoes which are injured 

 and infested with Phytophthora are capable of sprouting like healthy 

 specimens, and even producing entirely healthy shoots and plants. 

 While examining diseased tubers of this kind which had sprouted, I 

 had often, after they were shrivelled, found, in tlu? tissue which con- 

 tained the Phitophthora, bodies which, it might be supposed, were 

 oospores of a Peronospora or a Saprolegiiia. On the other hand, I 

 had observed in several previous experiments witli diseased tubers a 

 condition of the mycelium which seemed to promise a positive result. 

 It is known that the starch contained in the healthy colourless tissues 

 of the sprouting tuber is gradually reduced in quantity, and that the 

 large cells become filled with watery licjuid. Owing to this the 

 whole structiire becomes watery-transparent : it remains at first turgid 

 and firm, then afterwards it collapses and decay takes place. In the 

 diseased tubers this phenomenon occurs in the tissues which have re- 

 mained healthy, and which are principally found in the centre of 



* "Zeitschriftdes landwirthschaftliohen Central- Vereinsd.Provinz Sachsen, " 

 1870. No. 12. 



