598 FUNGI IMPERFECTi: THE IMPERFECT FUNGI 



They are stiff, and usually septate and bear at the apex a long, obclavate, 

 sometimes slenderly tapering conidium, which is usually multiseptate. As 

 in Ramularia as soon as the conidium is formed another forms closely 

 below it on a short branch which pushes up beyond the first scar of co- 

 nidial attachment, so that the apical portion of an old conidiophore is 

 crooked and marked by numerous scars. The over 500 species are with 

 few exceptions parasitic in the green tissues of the host plants on which 

 they produce characteristic leaf spots. Cercospora heticola Sacc. causes a 

 very destructive leaf spot disease of beets {Beta vulgaris L.), especially the 

 sugar beet. A leaf spot of cherry is caused by C. ceraseUa Sacc. which has 

 been shown to be the conidial stage of Mycosphaerella ceraseUa Aderh. C. 

 apii Fr. is the cause of the early blight of celery {Apium graveolens L.). Of 

 the many hundred described species of Cercospora and Cercosporella the 

 perfect stage is known for only a few. (Fig. 20 lA.) 



Family Stilbellaceae. In many of the Moniliaceae, especially in the 

 genus Penicillium, under certain conditions of growth the conidiophores 

 will be massed together into columns, coremia, from whose upper portion 

 the conidiophores spread out and produce their conidia. What is here a 

 response to special conditions is the normal condition in the Stilbellaceae. 

 The coremium or synnema may be relatively short, the upper half or more 

 being covered by the spreading tips of the conidiophores, or these may 

 appear only at the top, the closely united hyphae producing no spore- 

 bearing branches except at their upper ends. In Isaria the upright, simple 

 or branched, colorless coremia are covered from near the base to the apex 

 by slender hyphae bearing terminally the single, small, spherical or ellip- 

 soidal, hyaline, one-celled conidia. Many of the species grow saprophyti- 

 cally on plant tissues but a few grow on insects, probably in many cases 

 parasitically. These latter may be the conidial stages of species of Cordy- 

 ceps of the Hypocreales. In Graphium the coremium is dark-colored and 

 the spore-bearing head is only at its top. The conidia are hyaline or almost 

 so, ovoid or ellipsoid, not in chains, the whole head l^eing enclosed in a 

 drop of slime. (Fig. 203C.) Such fungi are mostly insect distributed. Some 

 species are the conidial stages of Ophiostoma (Ceratostomella) of the Asco- 

 myceteae. Most destructive is G. ulmi Buis. whose perfect stage is 0. ulmi 

 (Buis.) Nannf., the cause of the so-called Dutch elm disease, so destruc- 

 tive to American elm (Ulmus americana L.) in America. For the majority 

 of species the perfect stage is unknown. In the genus Stysanus the co- 

 remial stalk is colored and as in Graphium the conidia are light-colored or 

 hyaline. They are borne in chains, covering the upper half or so of the 

 fruiting body. Most of them are saprophytic but some are suspected of 

 being weak plant parasites. Perfect stages are unknown. (Fig. 203B.) 



Family Tuberculariaceae. The genera customarily assigned to this 

 family are almost certainly not closely related. The conidia are borne on 



