286 FUNGOUS DISEASES OF PLANTS 



Melanconiales — conidia borne on relatively short conidiophores 

 arising from or within a more or less differentiated stroma, pro- 

 duced usually beneath the epidermis. 



Sphceropsidales — conidia borne on short conidiophores arising 

 within a perithecium, or pycnidium, or sometimes within cavities 

 of a dense stroma. 



The primary subdivisions of these groups are termed families, 

 and in the case of the Sphaeropsidales this classification is based 

 on characters more or less comparable to those separating certain 

 orders or families of the Ascomycetes. The secondary and further 

 subdivisions down to the genera are properly an artificial classifi- 

 cation based chiefly upon the color of the spores and the extent 

 of septation. Details of this classification may be found in the 

 taxonomic works ; but a brief comparison of important genera 

 embracing parasitic species is here included. 



I. HYPHOMYCETES 



I . {Mucedinece ; mycelium and spores generally light colored.) 



Oospora. In this genus the vegetative mycelium is delicate and 

 inconspicuous. The conidia are relatively numerous, ovoidal to 

 spherical in form, hyaline, and unicellular (amerosporic). 



Monilia. In this case the vegetative hyphse are more evident 

 and the fertile hyphse are branched, often in dense clusters, with 

 hyaline or slightly colored conidia produced in chains. To this 

 form genus the conidial stage of the brown rot of stone fruits 

 may be referred (cf. Sclerotinia fructigend). 



Oidium. As generally interpreted this genus includes among its 

 representatives the conidial stage of Erysiphaceae (cf. page 215). 

 The powdery mildew of the vine was long known only as Oidium 

 Tuckeri. The conidia are produced in chains on short, erect 

 hyphae generally arising from a superficial mycelium. 



Sporotrichum possesses an extensive mycelium and conidio- 

 phores which are, as a rule, well differentiated. The latter are 

 branched and bear numerous, hyaline, one-celled, more or less 

 spherical conidia. These originate from tips of branches or on 

 minute sterigmata. Some species of this genus parasitic or sapro- 

 phytic upon insects are connected with a compound form, Isaria, 

 and an ascigerous stage, Cordyceps. 



