MICROSCOPIC AhGM AND FUNGI. 207 



f/enus with certain fresh-water Algae. Whence it follows that 

 that class in general is not a natural group, but an assemblage 

 of plants of various natural families and genera, joined 

 together by a single artificial character. 



In this way the Cryptococcaceae will be arranged under the 

 Palmellaceae ; the Septomiteae, under the Oscillarieae and 

 Septotricheae ; the Saprolegnieae under the Vaucherieae ; some 

 genera would be abolished altogether, such as Hygroci'ocis, 

 whose species must be regarded as colourless species of 

 Leptothnx, and those of Beggiatoa as colourless Oscillarice : 

 and as Spirochcete, which is identical with Spirulina plicatilis ; 

 Vibrio bacillus would probably be termed Oscillaria bacillus^ 

 &c. 



2. Cohn's observations on the subject of Chytridium and 

 some allied genera are of particular interest in several respects, 

 and especially with reference to the important matter of the 

 connexion between parasitic Fungi and certain diseased condi- 

 tions in plants. The extraordinary prevalence, of late years, of 

 epidemic diseases attacking nearly all cultivated plants, and 

 many of which have been observed to be accompanied with 

 the development of Fungi, renders the determination of the 

 true relations of the one to the other a point of extreme 

 interest and importance, not only in a scientific, but also in an 

 economical sense. To the ancient and well-known pests of 

 ' rust ' and ' smut ' have been added, it may be said, within 

 a few years, the more destructive potato — and vine — cisease ; 

 but other important cultivated plants, as the olive — orange — 

 beet-root, as well as timber-trees, belonging to the Coniferous 

 family especially, have also suffered in a similar way. 



Disease of this kind has been by no means confined to 

 cultivated plants — these epidemics are not limited to plants 

 useful to mankind — their ravages may be witnessed among 

 the useless and noxious members of the vegetable kingdom, 

 to an almost equal extent with the highly-prized objects of 

 human cultivation. 



A remarkable instance of this is afforded in the present 

 Memoir of Cohn. And his observations will go very far to 

 solve any remaining doubts as to the true nature of the 

 relations between the parasite and the disease. Inasmuch as 

 the victim and the destroyer are both plants of the simplest 

 kind — in fact, unicellular algae, in which the whole process of 

 the invasion and its effects is plainly submitted to the eye. 

 The main question to be determined is, whether the fungus is 

 to be regarded as the cause of the disease, or whether the 

 disease is, as it may be termed, the cause of the fungus. In 

 the former case, the appearance of the Fungus or its spores 



