398 THE DEUTEROMYCETES (FUNGI IMPERFECTI) 



The closely related Genus Heterosporium was recently studied 

 by Jacques (1941). The well-known H. iridis on Iris is geneti- 

 cally connected with DidyuieU'ma macrospora. Jacques secured 

 the perithecial stage in culture on sterile iris leaves. He found 

 that H. omithogali is the conidial stage of Didyntellina orni- 

 thogali. The developmental cycle of other important pathogens, 

 including H. phlei on Fhleinn pratense, H. echimdatum on Dian- 

 thiis caryophylhis, and H. variable on Spinacea oleracea, should 

 be ^iven consideration. 



The two genera Alternaria and Alacrosporium, which are re- 

 garded as synonymous by some and which are at least closely 

 related to each other, have bottle-shaped conidia that are both 

 transversely and longitudinally septate. The basal end is the 

 larger. The conidiophores are stout, short, lateral hyphal 

 branches. In Alacrosporium the conidia are produced singly; in 

 Alternaria they form chains, the basal conidium being the old- 

 est. The features possessed by these genera that are of taxonomic 

 value are given consideration by Elliott (1917). 



A few species of Alternaria have been demonstrated to have 

 Pleospora as their perfect stage. Among the better-known 

 species parasitic on plants are Alternaria solani, causing early 

 blight of potatoes, A. tenuis and A. longipes, pathogenic to to- 

 bacco, A. citri, occurring on citrus, A. paiwx, found on ginseng, 

 and A. brassicae var. nigrescens, which seriously blights the fo- 

 liage of cantaloupes. 



Cercospora is undoubtedly the largest genus of the Dema- 

 tiaceae, and its species are very destructive to cultivated plants. 

 One or more species of Cercospora have been recorded as para- 

 sites on practically every crop species and on many kinds of wild 

 plants as well. The studies by Lieneman (1929) and Solheim 

 (1929) give especial attention to taxonomic problems involving 

 this genus. Its conidiophores are typically fasciculate and emerge 

 from the stomata. The upper portions are covered with numer- 

 ous scars left after the falling of the slender, clavate, septate co- 

 nidia. Several species of Cercospora, such as C personata on 

 peanuts, C. bolleana on figs, C. viiisae on banana, and C. lythra- 

 ceannn on pomegranates, have been demonstrated to be imper- 

 fect stages of Mycosphaerella. Cercospora beticola, especially 

 destructive to sugar beets, and C. nicotianae, producing frog-eye 



