DISEASES CAUSED BY FUNGI 43 



are included, to give a few examples, Oidium, Cephalosporium, 

 Aspergillus, Penicillium, Botrytis, Sporotrichum, Verticillium ; 

 in the Dematiaceae : Thielaviopsis, Cladosporium, Helmintho- 

 sporium, Alternaria, and Cercospora 



The third family, Stilbaceae, consists of forms in which 

 several or many of the fertile hyphae are collected into a compact 

 bundle to form the conidiophore, the conidia being borne in a 

 head or tuft at the top or sometimes along the sides. Stilbella 

 (or Stilbum) which includes the conidial forms of Sphserostilbe, 

 Graphium, which similarly includes the conidial form of Rosel- 

 linia, Isaria, which has many species parasitic on insects, and 

 Gibellula, parasitic on spiders, are examples. 



In the fourth family, Tuberculariaceae, the fertile hyphae, 

 together with an admixture of sterile hyphae, are gathered into a 

 rather compact body known as the sporodochium, which may be 

 globose, discoid, or form a somewhat irregular crust. Often 

 the hyphae are more or less radially arranged. The consistency 

 of the mass is often waxy or gelatinous, may be horny, or may be 

 merely made up of threads more or less embedded in mucilage. 

 The family is in many respects a vaguely defined one. Its most 

 important parasitic genus is Fusarium. iEgerita, the white-fly 

 fungus, is another example. 



A further section of the Fungi Imperfecti, the Sterile Mycelia, 

 consists of those fungi for which not even a conidial form of 

 reproduction is known. The important sclerotium-forming 

 parasites Rhizoctonia and Sclerotium remain here. Himantia 

 stellifera, a mycelium on the roots of sugar-cane, will probably 

 be shown to belong to Odontia, a basidiomycete. 



The genus Graphiola, parasitic on palms, of which G. 

 phcenicis occurs on probably every date-palm in the West 

 Indies, remains unclassified, though it produces spores. It 

 is so individual in form that no relationship to other fungi can 

 be established. 



Systematists differ somewhat in regard to the classification 

 of fungi ; the following arrangement, which aims at simplicity, 

 is based on the system of Engler and Prantl. The positions both 

 of the groups of parasites mentioned in this chapter and of com- 

 mon saprophytes are indicated. It will be noticed that in this 

 scheme the Perisporiales are included in the group Pyrenomy- 

 cetes, which is characterised by having the asci enclosed in a 

 perithecium. In most recent classifications the Perisporiales are 

 treated separately, as has been done on p. 37. 



Myxomycetes (slime-moulds). 

 ScHizoMYCETES (bacteria). 

 EuMYCETES (all other fungi). 



Class I. Phy corny cetes. 



{a) Oomycetes (downy mildews). 



[h) Zygomycetes (moulds like Mucor). 



