596 FUNGI IMPERFECTi: THE IMPERFECT FUNGI 



phores, causing spots on leaves and decayed spots on the fruits of the 

 cucumber, Cucumis sativus L. Upon the leaves of the tomato one often 

 finds brown- or violet-colored, velvety patches sometimes quite large. 

 These are the conidia and conidiophores of C. fulvum Cke. In this species 

 the conidiophores are but little branched. In both the latter species the 

 conidia rarely if at all appear in chains and are always once septate. 



Among the phragmosporous Dematiaceae the genus Helmintho- 

 sporium includes several species that are harmful to cereal crops. The 

 upright, unbranched or branched, septate conidiophores arise usually 

 several from a stoma and bear terminally, and less often laterally as well, 

 the more or less cylindrical or obclavate, multiseptate, brown conidia. 

 The infection may be systemic, the mycehum pervading almost the whole 

 plant, or the infected areas may be limited, forming rounded or elongated 

 leaf spots. For most of the species no perfect stage is known. The perfect 

 stage of H. teres Sacc, the cause of the net blotch of barley, is Pyrenophora 

 teres (Died.) Drechs., one of the Pseudosphaeriales. (Fig. 96 A.) The genus 

 Heterosporium has shorter conidiophores and ellipsoid, roughened spores, 

 usually single at the apex of the conidiophore but sometimes in short 

 chains. The perfect stage of H. gracile (Wallr.) Sacc, cause of leaf spots 

 and killing of leaves of Iris, is Didymellma iridis (Desm.) v. Hohn., also 

 of the same order as the foregoing. The perfect stages of the remaining 35 

 or 40 species of Heterosporium are unknown. There are many other genera 

 of the phragmosporous Dematiaceae, e.g., Dendryphium, with dendroi- 

 dally branched conidiophores and the conidia single or in short chains, 

 Napicladium, with short, weak conidiophores and large terminal conidia, 

 some species parasitic and others not. 



The dictyosporous genera of this family are largely saprophytes. Their 

 conidia are septate transversely and to a certain degree longitudinally 

 as well, and occur singly or in chains on short or long, unbranched or 

 branched, stiff or weak conidiophores. In Alternaria the conidiophore is 

 rarely branched and the conidia are produced in acrogenously developing 

 chains or singly. The apical portion of each conidium is narrowed and 

 often much elongated, bearing at its tip the next narrowly or broadly 

 ovoid, tapering conidium. In the older literature a distinction was made 

 between Alternaria and M acrosporium with conidia single at the apex of 

 the conidiophore. It was shown, however, by Wiltshire (1933, 1938), 

 Groves and Skolko (1944a and b) and by Neergaard (1945) that the 

 latter name was first used for species with catenulate spores and only 

 later for those with spores i)roduced singly. Therefore they proposed that 

 the name be dropped and Stemphylium be used for some species called in 

 literature by the name Macrosporium. Those forms with spores tapering 

 at the upper end should be called Alternaria, even when they may usually 

 fail to produce chains. Stemphylium has its spores rounded at both ends 



