362 
On the Potato Disease- 
potatoes also ; but in order to produce the disease of last season, 
as justly observed by M. Decaisne, it must have attacked every 
plant, \\\\\c\i it certainly did not; fori most carefully examined 
the leaves and stalks of several crops last year at several 
intervals, with an excellent glass, without meeting it, except 
upon one occasion. We are also informed that the most skilful 
observers* on the Continent had examined whole fields without 
perceiving the least trace of this fungus ; and M. Desmazieres 
states that he had not been able to perceive more than five or 
six "boutons" ofbotrytison many hundreds of infected potatoes. 
I have also examined a large quantity continually, and have very 
rarely met with any mildew at all resembling it, although other 
kinds were common. I cannot help thinking, therefore, from the 
recent discovery of this minute parasite, that its peculiar habits 
have been laid down with too much precipitation, sufficient time 
not having elapsed to afford proper opportunities of ascertaining 
whether it really was so much more dainty than others of the 
same family or not. I have met with certain cases which lead 
me to think it is not so. In March last I procured several dis- 
eased plants from a market-gardener, and, having placed one of 
the old sets on the border of a late vinery, in a few days a tuft of 
mildew appeared on it, the plants of which closely resembled a 
drawing of the botrytis infestans made from a leaf kindly sent me 
by Mr. Berkeley himself The set was then in a moist state of 
decay. I also found a similar fungus on the llth of April on 
some shoots pulled off diseased potatoes, and sent me from Syden- 
ham, which had been lying on the same border ever since the 
10th of February, being of course quite dead and brown. But 
what is still more remarkable, I found on the llth of April a 
mildew in similar tufts, spreading over the mould in a flower-pot 
in which I had planted a diseased potato for the sake of experi- 
ment, and by sprinkling a httle more moist earth over it I kept it 
still increasing for upwards of five weeks, although numbers of 
minute insects of the genus called Podura fed upon it as it became 
older, and q\jite consumed it. Many of these plants, as viewed 
under an ordinary microscope, could not be distinguished from 
those on the potato-leaf; but Mr. Berkeley, to whom I sent a 
portion of the mould, found two distinct species upon it, but did 
not consider either to be the true botrytis infestans ; and I have 
since been able to satisfy myself that one of the species is not 
identical with that; and from Mr. Berkeley's high character, 
little doubt can be entertained as to the other. It may, however, 
be observed, that a wide difference exists in the several specimens 
of botrytis infestans with which Mr. Berkeley's memoir is illus- 
* MM. Decaisne, Leveille, Thuret, &c. 
