Researches into the Nature of the Potato-Fun ff us. 
259 
with the smooth globules cannot at the present time be more 
exactly determined. 
8. I had arrived at these results when the notice contributed 
to 'Nature' (July 22, 1875), by Mr. Worthington G. Smith, on 
the oospores observed by him in the potato-fungus, reached me. 
Afterwards I became acquainted with his publications in the 
' Gardeners' Chronicle,' and in the ' Journal of the Royal 
Agricultural Society ' (1875), all of which I may be allowed to 
consider as known to my readers. 
I will now confess that my reason for relating the history of 
Pi/thium vexans and Artotro(/us so minutely was that I wished 
to show clearly, by an example, how, without the greatest care 
in researches of this kind, one may be led into great error, 
and especially in what way criticism ought to be applied in 
examining these observations. Let me then examine closely and 
critically the statements of Mr. Smith. 
Mr. Smith describes two kinds of bodies. First, brown, warty 
Ijodies, which had been named Protomyces by Mr. Berkeley, 
and were found in the brown spots of potato-leaves infested 
with fungus. In form and size, and in the appearance of their 
membrane, they have a great similarity to the oospores of 
Peronospora Arenarice, Berk. (' Nature,' p. 234, fig. E, F ; ' Gard. 
Chron.,' Fig. 19, e). On this ground the bodies were regarded 
as oospores of a Peronospora. They occur on the leaves of 
potatoes, on which no other Peronospora is known except 
P. infestans ; and mycelium occurs along with some conidio- 
phores on the same brown spot as the warty bodies, therefore 
the author believes that they belong to P. infestans. There 
is no distinct evidence for this, not even if we admit that the 
mycelium and conidiophores in the warty bodies actually belong 
to P. infestans. But fig. 19, quoted above, renders this verv 
doubtful, since the conidiophores (f) present an important 
difference from those of the real P. infestans; and even as 
regards those which Mr. Smith figures, ' Gard. Chron.,' p. 68, 
Fig. 9, C, I cannot accept the accompanying statement, that 
they are the organs mentioned as of P. infestans, for it is 
clear from the text on p. 68 of the ' Gard. Chron.,' that the 
author does not accurately know the conidiophores of the 
potato-fungus. I cannot, therefore, hold that it has been posi- 
tively proved that these warty bodies are oospores, or even that 
they belong to P. infestans. Still, it may be admitted that 
both these opinions may be correct. Looking still further at 
the author's description, I find that the bodies occurred very 
sparingly in the places named. But when, for the purpose 
of isolating them, the material was placed in water, mycelium 
grew and ramified luxuriantly in the rotten tissue of the potato, 
s 2 
