Researches into the Nature of the Potato -Fungus. 265 
other plants which disappear in the autumn and return again in 
the summer, though we know that they do not entirely disappear 
in winter, but last through it in some form or other — mostly un- 
apparent. These phenomena being everywhere confirmed, we 
ought not to assume that the potato-fungus is perpetuated in a 
different manner. If we cannot find hibernating oospores be- 
longing 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 atten- 
tion 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 Phytophthora. 
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 myce- 
lium 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 store- 
rooms the conidiophores may burst their way through the un- 
broken 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 develop itself in 
them.' All this is obvious from simple experiments which have 
been well-known for a long time. 
We have thus two ways in which the living fungus that has 
survived the winter, may in the spring find its way to the fields 
with the seed. The second is, perhaps, the more usual way ; 
at all events, it is the more dangerous, because, even with great 
care in the choice of seed, it cannot be avoided with certainty. 
In both cases the fungus is placed in the earth along with the 
tuber, and cannot there leave it ; the fungus must die and 
become corrupt in and with the tuber. It can, however, find 
. • " Reeherclies sur le Developpement de quelques Champignons parasites." 
' Annales de Sciences Naturelles,' vol. sx., 186:5, p. 1. 
