MOULDS. 153 



PeronosjQora mfestans, or, as it was at first called, 

 Botrytis infest ans ; but on a revision of tlie genera 

 Botrytis and Peronospora, it was transferred to the 

 latter genus, in which it remains. Three names were 

 given to it, within a short period of each other, 

 by different mycologists, in ignorance of its having 

 already received a name. The one we have adopted 

 appears to have the priority, at least of publication, 

 and was given by Dr. Montague. That of Botrytis 

 devastatrix was given by Madame Libert, and 

 Botrytis fallax by M. Desmazieres. The principal 

 feature in this species seems to consist in the 

 branches becoming alternately thickened and con- 

 stricted, so as to resemble a moniliform string or 

 yiecklace of little bladders or vesicles. The branches 

 are also more erect than in the allied species, and 

 the spores are solitary on the tips or from the sides 

 of the branches, and not in pairs or clusters, and 

 the tips are simple, and not bifid or trifid, as in 

 most of its allies. It need scarcely be remarked, 

 that a high power of the microscope is necessary 

 to make out the distinctive features of the difierent 

 members of this genus, and that to the naked eye 

 they only appear as a minute whitish mould. As 

 already stated, this little fungus makes its first 

 appearance on the under surface of the leaves, 

 especially the lower ones, of the potato plant, and 

 afterwards attacks the stem, and ultimately the 

 tuber. For examination it is better to select the 



