i9i 2] WOLF—ACTINONEMA ROSAE 221 



simulating the blotch on the leaves. Conidia are formed readily 

 on the ends of the hyphae. Such conidia are often so strongly 



um 



that each cell is round. There is, then, 

 little surface of contact between the cells and they are readily 

 separable one from the other. These spherical halves germinate 

 in the normal manner (fig. 2). Acervuli apparently like those on 

 the leaves are also formed on bean pods in the blackened areas. 

 These bear conidia like the typical ones from rose leaves. 



Systematic position of the conidial stage 



The genus Actinonema is usually placed by systematists in 

 the Sphaeroidaceae. 2 This family is a group of imperfect fungi 

 possessing a pycnidium of the type present in Ascochyta, Sphaerop- 

 sis, etc. The pycnidium or conceptacle is more or less oval in form, 

 with a membranaceous wall of fungous tissue, usually opening at 

 the apex by a minute pore. Some writers speak of the fruit bodies 

 of Actinonema as pycnidia 3 or perithecia. 4 Frank 5 considered 

 them as very flat spermagonia ("des sehr flachen Spermagoniums"). 

 Sorauer 6 speaks of them as small astomate pycnidia ("die kleinen 

 miindungslosen Pykniden ' ') . 



It is very evident from the foregoing account that the conidial 

 stage of the rose Actinonema is not of the type in which the conidia 

 are borne in a pycnidium or perithecium. The conidia are borne 

 in an acervulus resembling that found in the Melaneoniales, as 

 exampled by Gloeosporium, Marsonia, etc. Scribner 7 has correctly 

 figured the structure of the acervulus and says that while the 

 fungus from analogy is placed with the sphaeriaceous fungi, no 

 penthecia-like or pycnidial structures have been observed. 



Partly because of the different interpretations of the morphology 



2 Saccardo, P. A., Syll. Fung. 3:408. 1884; also Lixdau, G., Sphaeropsidales 

 m Exgler and Prantl's Pflanzfam. 1:369. iqoo. 

 3 Lixdau, G.Joc. cit. 



Massee, G., Diseases of cultivated plants. 428. iqio. 



s Frank, A. B., Die Krankheiten der Pflanzen. 621. 1880. 



Soravf.r, Paul, Handbuch der Pflanzenkrankheiten. 406. 1908. 



7 Scribner, F. L., The black spot on rose leaves. Kept. U.S. Dept. Agric. 

 366-369. pi s , 8 , 9. d88 7 ) 1888. 



