Now, it is 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.
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