122 roTATO-FnfGUs. 



are locally associated, and which were more easily confused with each 

 other tliirty years ago than appears credible to us now. The specific 

 name hi/d>iosporus shows that Montague had drawn it chiefly from 

 the prickly form. The other form 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 

 Pythium vexans and Artotrogtis ?>o 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 c^pecially in what 

 way criticism ought to be applied in examining thes ; observations. 

 Let me then examine closely and critically the : tatements of Mr, 

 Smith. 



Mr. Smith describes two kinds of bodio-. First, brown, warty 

 bodies, which had been named Trotomyces 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) [" Journ. 

 Bot.," 1875, p. 341, fig. 4]. 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 conidiophores on the same brown 

 spot as the warty bodies, tlierefore the author believes that they belong 

 to P. infestari". There is no distinct evidence for this, not even if we 

 admit that the mycelium and conidiophores in the brown spots 

 actually belong to P. infestans. But fig. 19, quoted above, renders 

 this very doubtful, since the conidiophores (i') present an important 

 diffeience from those of the real P. infestans; and even as regards 

 those which Mr. Smith figures in " Gard. Chron.," p. 08, fig, 9, c 

 ["Journ. Bot.," p. 339, fig. 1], I cannot accept the accompanying 

 statement that they are the organs mentioned as of P. infestayis, for it 

 is clear from the text on p. 68 of the " Gard. Chron." that author 

 does not accurately know the conidiophores of the Potato -fungus. I 

 cannot, therefore, hold that it has been positively proved that these, 

 warty bodies are oospores, or even that they belong to P. infestans. 

 Still, it may be admitted that both these opinious 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 pur- 

 pose of isolating tliem, the mateiiul was placed in water, mycelium 

 grew and ramified luxuriantly in the rotten tissue of the Potato, and 

 produced the numerous bodies which are described as the oogonia, 

 antheridia, and oospores of the Potato- fungus. These are the second 

 subject in the author's description. If the representations given are 

 correct, these objects do not belong to the Potato-fungus, and cannot 

 well be oogonia, antheridia, and oospores. I confine myself here to 



