right to say that, with respect to the mode of spread of the
disease, scientific men are not quite agreed. All admit that it may be
conveyed by contact, that one leaf may infect its neighbors, and that
birds, flies, rabbits, and other ground game may carry the disease from
one plant to another and from one crop to another. This is insufficient
to account for the sudden onset and the wide extent of potato
"epidemics," which usually attack whole districts at "one fell swoop."
Some of those best qualified to judge believe that the spores are carried
through the air, and I am myself inclined to trust in the opinion
expressed by Mr. William Carruthers, F.R.S., before the select committee
on the potato crop, in 1880. Mr. Carruthers' great scientific
attainments, and his position as the head of the botanical department of
the British Museum, and as the consulting naturalist of the Royal
Agricultural Society, at least demand that his opinion should be received
with the greatest respect and consideration. Mr. Carruthers said (report
on the potato crop, presented to the House of Commons, July 9, 1880,
question 143 _et seq._): "The disease, I believe, did not exist at all in
Europe before 1844.... Many diseases had been observed; many injuries to
potatoes had been observed and carefully described before 1844; but this
particular disease had not. 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 18