240 FUNGI. 



detected. JEcidiwm compositarum and JEci&ium ranunculacearum, 

 for instance, are found on various composite and ranuncnlaceous 

 plants, and as yet no sufficient evidence has been adduced to 

 prove that the different forms are other than varieties of one 01 

 the two species. On the other hand, it is not improbable that 

 two species of Mcidium are developed on the common berberry, 

 as De Bary has indicated that two species of mildew, Puccinia 

 graminis, and Puccinia straminis, are found on wheat. 



Htphomycetes. — The moulds are much more universal in their 

 habitats, especially the Mucedines. The Isariacei have a pre- 

 dilection for animal substances, though not exclusively. Some 

 species occur on dead insects, others on decaying fungi, and the 

 rest on sticks, stems, and rotten wood. The Stilbacei have also 

 similar habitats, except that the species of Illosporium seem to be 

 confined to parasitism on lichens. The black moulds, Dematiei, 

 are widely diffused, appearing on herbaceous stems, twigs, bark, 

 and wood in most cases, but also on old linen, paper, millboard, 

 dung, rotting fruit, &c, -whilst forms of Cladcsporium and Macro- 

 sporiwm are met with on almost every kind of vegetable substance 

 in which the process of decay has commenced. 



Mucedines, in some instances, have not been known to appear 

 on more than one kind of matrix, but in the far greater number 

 of cases they flourish on different substances. Aspergillus 

 glaucus and Penieillium crustaeeum are examples of these uni- 

 versal Mucedines. It would be far more difficult to mention 

 substances on which these moulds are never developed than to 

 indicate where they have been found. With the species of 

 Peronospora it is different, for these are truly parasitic on living 

 plants, and, as far as already known, the species are confined to 

 certain special plants, and cannot be made to vegetate on any 

 other. The species which causes the potato murrain, although 

 liable to attack the tomato,, and other species, of Solanacees, does 

 not extend its ravages beyond that natural order, whilst Pero- 

 nospora parasitica confines itself to cruciferous plants. One 

 species is restricted to the TJmhellifera, another, or perhaps two, 

 to the Leguminosm, another to Rubiacem, two or three to Sanun- 

 nitlacew, and two or three to Caryoplxyllacecd. All the experi- 



