288 FUN<;<H S DISKASKS OF PLANTS 



Helminthosporium possesses straight, dark colored conidio- 

 phores bearing club-shaped or spindle-form, many-celled, flavous 

 to dark colored conidia (phaeophragmic). 



Macrosporium. In this genus the straight conidiophores bear 

 ovoidal or elliptical spores which are transversely septate, and 

 many of the cells thus formed become longitudinally, and then 

 even again transversely, divided (dictyosporic). 



Alternaria differs from the previous genus particularly in hav- 

 ing the conidia borne in chains, and these conidia are often 

 clavate in form. 



Cercospora possesses straight, flexuous, or strongly geniculate 

 conidiophores, which may be single or grouped. The conidia 

 are needle-shaped or filiform (scolecosporic), hyaline to considera- 

 bly colored, and from three to many times septate. This is one 

 of the largest genera of the Hyphomycetes, containing about five 

 hundred described species, more than three fourths of which are 

 attributed to North America. All species are parasitic. 



3. ( Tubercnlarice ; conidiophores in the form of a tuberculate 

 mass, or sporodochium). 



Volutella. In this genus the sporodochium, or fruiting tubercle, 

 is a more or less closed, disciform body, not, however, produced 

 on a basal stroma. It is provided, around the border, with hair- 

 like setae. The conidiophores are mostly unbranched and give 

 rise terminally to hyaline, unicellular conidia. 



Fusarium. In this genus the sporodochia are small cushion- 

 like masses of interwoven hyphae which may appear waxy or fila- 

 mentous in texture. The conidiophores proper are unbranched, 

 and they bear successively at the tips curved or sickle-shaped, 

 hyaline, many-celled (at maturity) conidia. 



II. MELANCONIALES 



Glceosporium. The spore-producing pustule, or acervulus, may 

 be extensive, and is made up of a mass of relatively short conidio- 

 phores arising from, and commonly partially inclosed within, a 

 stromatic cushion of fungous tissue. At maturity the stroma 

 opens, and thus it ruptures the . epidermis. It may even expand 

 so widely as to seem to constitute merely a basal stroma. The 

 spores are ovoidal, fusiform, or slightly curved, and hyaline 



