It is due to a species of plant, and although
that species is small, it is as easily separated from allied plants as
species of flowering plants can be separated from each other. This plant
was known in South America before it made its appearance in this country.
It has been traced from South America to North America, and to Australia,
and it made its first appearance in Europe in Belgium, in 1844, and
within a very few days after it appeared in Belgium, it was noticed in
the Isle of Wight, and then within almost a few hours after that it
spread over the whole of the south of England and over Scotland.... When
the disease begins to make its appearance, the fungus produces these
large oblong bodies (_conidia_), and the question is how these bodies are
spread, and the disease scattered.... I believe that these bodies, which
are produced in immense quantities, and very speedily, within a few hours
after the disease attacks the potato, are floating in the atmosphere, and
are easily transplanted by the wind all over the country. I believe this
is the explanation of the spread of the disease in 1844, when it made its
appearance in Belgium. The spores produced in myriads were brought over
in the wind, and first attacked the potato crops in the Isle of Wight,
and then spread over the south of England. The course of the disease is
clearly traced from the south of England toward the midland counties, and
all over the island, and into Scotland and Ireland.
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