ON THE PERONOSPOR^, 207 



cases the oospores, instead of producing zoospores, produced a 

 thick jointed thread, resembUng the threads of P. infestans^ and in 

 both cases the myceHum produced conidiophores and small 

 conidia, which were believed to be those of P. ijifestans. 



De Bary had remarked that supposing the warty bodies seen 

 by Worthington Smith were the resting spores^ they could not play 

 an important part in the life-history of the plant on account of 

 their extraordinary rarity. Worthington Smith now points out that 

 in his first experiments the resting spores were certainly rare, but that 

 afterwards they were produced in myriads, and that within the 

 tissues of a comparatively few leaves. De Bary had also further 

 objected that the fungus he had called Pythiimi vexans would 

 grow freely on the bodies of mites, etc., and that Peronospora 

 would not do so. Smith says he has observed the Peronospora 

 on the bodies of aphides — not only the threads, but also oogonia 

 and antheridia in conjugation. Worthington Smith's experiments 

 were repeated by Messrs. Broome, Vize, and Plo^vright, with 

 generally satisfactory results in confirming the original experiments. 

 Mr. Plowright observed resting-spores enclosed in the coils of 

 spiral vessels. 



Curiously enough, a drawing of the Potato fungus was made 

 in 1845 by G. H. O. Stephens, of Bristol, and in it a body of the 

 exact shape, size, and colour of the resting spore is depicted. He 

 drew what he saw under the microscope, but did not know its 

 import. A copy of this drawing is given in the Gardener's 

 Chronicle for 1877. In 1880, Worthington Smith writes as to the 

 non-rarity of the resting spores : — " They exist in uncountable 

 numbers in nearly every old exhausted Potato tuber belonging to 

 infected plants, and may be found most easily in any infected 

 Potato field in this country. Also, that although the mycelium 

 of nearly every fungus is able to go into a state of hibernation at 

 times, according to his experience it is very rarely found in the 

 Potato disease. Controversy, however, with regard to the 

 Potato disease seems never likely to come to an end, for the 

 battle is now shifted to other points." 



Berkeley long ago wrote as to the concluding stage of this 

 disease : — " The whole soon dries up, and in many instances 

 exhibits in the centre the black, irregular, fungoid masses which 



