330 BULLETIN OF THE BUSSEY INSTITUTION. 
much longer time to germinate than the asexual spores. Analogy, then 
ou the supposition that the potato rot isa true Peronospora, would lead 
us to search for the odspores in the substance, not on the surface, of 
the potato or some allied plant. The potato, however, has been so well 
searched by different observers, that, if the odspores are really there, it 
seems hardly credible that they should for so long a time have escaped 
observation. The more probable. supposition would be that the disease, 
as well as the potato, was imported from Peru, and that, in that coun- 
try, the Peronospora lives upon different species of Solanum, of which 
there are a good many that inhabit Peru, and that, although when’ 
growing on the potato only asexual spores are produced, yet, on other 
species of Solanum, odspores as well are found. If this last supposed 
species of Solanum has not yet been introduced into Europe or North 
America, that is a sufficient reason why we know nothing about the 
odspores. Until quite recently, this view has been adopted by many 
botanists. 
The migration of a fungus in the track of plants exported for culti- 
vation is not so improbable, as it might at first sight seem. In the case 
of the Peronospora infestans, we have no accurate record of the 
migration; but, within a few years, we have seen a good illustration, in 
the case of the so-called hollyhock fungus (Puccinia Malvacearum, 
Mont.), of what might happen in other cases. Some years ago Montagne 
described a fungus from Chili which was parasitic on certain species of 
mallows, and which he named Puccinia Malvacearum. At that time, the 
fungus was entirely unknown both in North America and Europe. A 
few years ago, a disease began to attack the hollyhocks, members of the 
mallows family, in the United States. This disease was found to be 
caused by the growth of Puccinia Malvacearum. A little later the 
same disease was noticed in England, and later in Central and South- 
ern France, where it attacked the common mallows of the field as 
well as the cultivated hollyhocks. In 1873 the fungus first appeared 
in the region of Strasbourg, and in 1874 it had advanced as far as 
Amsterdam in Holland, and Nuremberg and Erlangen in Germany. 
This instructive case shows that a parasitic fungus may spread over the 
world as readily as common weeds have done. 
But it may be that the potato-rot fungus is really not a Peronospora 
at all. It may be a fungus imitating, to a certain extent, the rust in 
grain, which passes through different stages, in one of which it lives 
