252 
The Potato Disease. 
their roots, but that they attach themselves to the stems or 
leaves, penetrating their epidermis or pushing their way through 
the stomates. 
It is to be hoped that the investigations on these fungi which 
will be undertaken in consequence of the offered prize, may lead to 
the discovery of these oospores in the Peronospora of the potato. 
As they are more especially rest-spores, supplying, along with 
the mycelium, the means of continuing the life of this species in 
a new season, their discovery and the determination of the part 
or parts of the plant in which they are produced may supply 
practical hints as to how to prevent the disease. Under any 
circumstances, however_, and in order to secure the destruction of 
the parasitic fungus, the diseased plants — whether leaves, stems, or 
tubers — should be destroyed by fire. Leaving them to decay on 
the field, or neglecting them in the farmyard and permitting them 
to get into the manure, is a certain means of maintaining these 
rest-spores (oospores) and mycelium in a state ready to germinate 
when the necessary conditions are present. 
It is further probable that when we have discovered the 
oospores in the potato fungus, which are known to exist in the 
other species of Peronospora, we shall not even then have 
ascertained the whole life-history of this parasitic fungus ; 
for the recent investigations of De Bary have shown that many 
of the microscopic fungi, which have hitherto not only been 
considered different, but have been classed under different groups, 
are really stages in the life of the same plant. In the analogous 
changes in the higher cryptogams, the spores are produced only 
at the final stage ; and among the different forms through which 
insects pass, only the imago or perfect insect has the power of 
continuing the species by producing eggs. But in these fungi 
each stage is spore-bearing. The investigations instituted for 
the offered prize may, it is to be hoped, disclose some stage 
in the progress of this parasite's life, where it can be more 
effectually dealt with than in that stage with which we are at 
present acquainted. 
De Bary has shown by experiment that there is nothing in one 
potato plant more than in another to predispose it to the attack 
of the fungus. It is not weak or unhealthy plants that are attacked, 
but wherever the spores rest, and, finding the suitable moisture, 
germinate, there the disease will appear. When once the fungus 
has got a footing in a crop of potatoes, its rapid growth, the little 
time required to develop fruiting branches, and the innumerable 
number of spores produced, make its progress very rapid. Even 
when the disease is first noticed by the cultivator", it has taken 
such a hold of the crop that its cure is, I believe, impossible. 
As moisture is so necessary to the development of the spores. 
