POTATO-FUNGUS. 125 



PytJimm vexaiis. These last organisms have a moderately thick mem- 

 brane, which in many cases is quite smooth, while in others the outer 

 surface is irregular, uneven, and of a very pale brownish-yellow 

 colour. Its protoplasm is shrivelled up into a small, round, central 

 body, no doubt in consequence of maceration. Some of these bladders 

 are still loosely surrounded with a very slender, irregularly folded or 

 shrivelled membrane, which alternately approaches the bladder or 

 retreats from it. It is only to these bladders that the terms oogonia 

 or oospores can be applied ; they have as little resemblance to tlie 

 figures in " Nature "(fig. e), and in " Gard. Chron." (fig. 19, d), as 

 to the oospores of P. Arenarm ; they might!rather be compared with 

 the thin-walled oospores of Peroriospora viticola, or with those of a 

 Pythiwm. But the preparations do not enable me to arrive at a certain 

 result as to what they really are. 



There might still be some light thrown on this subject, notwith- 

 standing all this uncertainty, if it were established that the organs in 

 dispute are .actually developed on the mycelium of the Potato-fungus, 

 and produced on its branches. The illustrations, however, which I 

 have examined, show the contrary. All the threads of mycelium in 

 fig. 13 possess numerous very regularly arranged septa. Now, it is 

 true that septa occur in the mycelium of P. infestans, especially when 

 old, but they are always isolated and very irregular. So long, also, 

 as the threads vegetate vigorously under water, they are for the most 

 part entirely without septa. No botanist could accept a mycelium of 

 the structure of fig. 13 as that of a Peronospora, unless the clearest 

 evidence for it were furnished from some other quarter. Further, 

 in the preparations examined by me I found, as already stated, the 

 globules without any connection with mycelium. 



In conclusion, I will state another objection, which, no doubt, if 

 it stood alone, would have little weight. Mr. Smith found his 

 oospores at an advanced stage of the process of maceration and decay 

 of the parts of the Potato in water. Now, so far as experience goes, 

 the Potato-fungus is exceedingly sensitive of decay, for as soon as this 

 is developed around it, it speedily dies, whether under water or in 

 the air. But, on the other hand, it is known that many other Fungi 

 do not begin to grow till decay has appeared. 



In the view of all these considerations I may, though with many 

 doubts, accept the warty bodies first described as perhaps the oospores 

 of P. infestans, but certainly not the forms found in the macerated 

 tubers. It however remains that Mr. Smith has described two forms 

 of Fungus in the macerated material, both difi'erent from the Potato- 

 fungus, and possibly also from each other. No one would have 

 thought of associating them with the Potato-fungus had they not been 

 found in parts of the Potato-plant when there was a great desire to 

 discover the oospores of that parasite. To what species of Fungus 

 the forms which are represented in the illustrations, and which occur 

 in the preparations, belong, cannot, for the reasons already repeatedly 

 stated, be determined ; indeed, the question has no further interest 

 for us here. 



9. It is thus apparent that we are not much further advanced 

 to-day than we were fifteen years ago in our knowledge of the mor- 

 phological peculiarities of the Potato-fungus. The warty bodies are 



