ar, a great reputation as a disease-resisting
potato; but all who have a practical knowledge of potato growing seem
agreed that we cannot expect its disease-resisting quality to last at
most more than twenty years from its first introduction (in 1877), and
that in time the constitution of the "Champion" will deteriorate, and it
will become a prey to disease.

There is some evidence to show, also, that the constitution of the potato
may be materially influenced by good or bad culture. Damp soils,
insufficient or badly selected manures, the selection of ill developed
potatoes for seed, and the overcrowding of the "sets" in the soil, all
seem to act as causes which predispose the potatoes to the attacks of the
parasite. Strong potatoes resist disease, just as strong children will;
while weak potatoes, equally with weak children, are liable to succumb to
epidemic influences.

The following account of some exact experiments carried out by Mr. George
Murray, of the Botanical Department of the British Museum, seems to show
that Mr. Carruthers' theory as to the diffusion of conidia through the
air is something more than a speculation:

"In the middle of August, 1876," says Mr. Murray, "I instituted the
following experiments, with the object of determining the mode of
diffusion of the conidia of _Peronospora infestans_.

"The method of procedure was to expose on the lee side of a field of
potatoes, of which only about two per cent, were diseased, ordinary
microscopic slides, measuring two inches long by one inch broad, coated
on the exposed surface with a thin layer of glycerine, to which objects
alighting would adhere, and in which, if of the nature of conidia, they
would be preserved. These slides were placed on the projecting stones of
a dry stone wall which surrounded the field, and was at least five yards
from the nearest potato plant. During the five days and nights of the
experiment, a gentle wind blew, and the weather was, on the whole, dry
and clear. Every morning, about nine o'clock, I placed fourteen slides on
the lee side of the field, and every evening, about seven o'clock, I
removed them, and placed others till the following morning at nine
o'clock. The fourteen slides exposed during the day, when examined in the
evening, showed (among other objects):

On the first day. 15 conidia.
" second day. 17 "
" third day. 27 "
" fourth day. 4 "
"