150 rOTATO-FUNGUS. 



first place to turn to would be the native land of the Potato-plant. 

 But no further observations need be made here on this subject, since 

 it unfortunately belongs only to the region of speculation. 



III. 



10. To the question raised at the beginning of section 3 (page 113), 

 concerning the hibernation of the Potato-fungus, and the manner in 

 •which it returns to the fields in summer, the researches described in 

 the foregoing pages supply no answer, or, at least, not one in any way 

 satisfactory. Even if the often-meKtioned warty bodies were hiber- 

 nating oospores of Phijtophthora, like the similar oospores of Perono- 

 spora Arenaria whicli resemble them, we should not gain much infor- 

 mation bearing upon these questions, since their occurrence is, at the 

 best, extraordinarily rare, while the Potato-fungus appears plentifully 

 every year. 



In all stages of the development and of the vital phenomena of the 

 Potato- fungus, as far as they are known, the parasite acts, apart from 

 the obvious specific peculiarities, precisely as many other plants which 

 disappear in the autumn and return again in the summer, though we 

 know that thoy do not entirely disappear in winter, but last through 

 it in some form or other — mostly unapparent. These phenomena being 

 everywhere confirmed, wo ought not to assume that the Potalo-fungus 

 is perpetuated in a diff'erent manner. If we cannot find hibernating 

 oospores belonging to it (like what are known in most of its allies), 

 another form of hibernation must be looked for and found. 



In a former publication* I was, perhaps, the first to call attention 

 distinctly to the fact that the mycelium of Phytophthora, like that of 

 parasites living in many other perennial plants, can be perennial in the 

 surviving parts of the host i.e., in the case of the Potato, in its tubers. 

 This has been repeatedly mentioned already, and is so easily tested by 

 simple and well-known experiments, that a short statement of it will 

 be enough here. 



In large stores of Potatoes we very often find some that are diseased, 

 i.e., containing the living mycelium of PhytophtJwra. It cannot 

 be disputed that the living Fungus may occasionally get into the field 

 through planting such diseased tubers. I do not say that this happens 

 largely; but, even if it never happened, the Fungus might still, quite 

 unobserved, get into the fields by means of diseased tubers, because, as 

 has been already said, the mycelium in the tuber forms conidiophores 

 directly it is placed in a moist atmosphere, and such a condition is 

 present in the usual temperature of spring. This may be easily seen 

 in fresh sections, or on the injured surfaces of a diseased tuber. In 

 moist storerooms the conidiophores may burst their way through the 

 unbroken skin, and particularly through the eyes. Should this occur, 

 even in one Potato, in one storeroom or cellar, it is clear that the 

 conidia will find their way to other Potatoes, and attach themselves to 

 them. If these quite healthy tubers should then be planted in the 

 ground, the conidia will germinate, the germs penetrate some of the 

 tubers, and the mycelium develope itself in them. All this is obvious 

 from simple experiments which have been well known for a long time. 



* " Recherches 8ur le Developpement de quelques Champignons parasites. 

 Annales de Sciences Naturelles," vol. xx., 1863, p. 1. 



