ROSE CANKER AND ITS CONTROL. 13 



sudden wilting and dying of shoots which have gi'own up rapidly from 

 below the surface of the ground. Older shoots are rarely killed outright. 

 Only occasionally have we seen entire plants killed by this disease. 

 One, several or all of the shoots of a plant may be attacked. Dead " brush " 

 and dead small shoots are usually much in evidence in affected houses. 

 The seriousness of the disease, however, lies not in the number of plants 

 killed but in the fact that affected plants are small and weaker, resulting in 

 diminished yields of inferior roses. The diseased plants cannot be forced, 

 no matter how much fertilizer is applied and how well they are cultivated. 

 New shoots do not grow from beneath the surface of the soil, but all 

 come from the tops. These latter symptoms are the ones which the 

 florist usually notices first, and, in fact, may be the only ones he notices. 

 Diagnosis of this disease is rendered difficult by two natural develop- 

 ments in the life of the rose plant which may easily be confused with 

 disease: (1) Many varieties of roses naturally turn black at the crown 

 very early; this, however, is a superficial blackening, and rarely runs 

 up much above the surface of the ground. (2) The bark of all rose stems 

 ' cracks with age, especially at the base, just as the bark of trees does. 

 These two developments often resemble canker so closely that even 

 one experienced in diagnosis may be misled. 



DESCRIPTION OF THE CAUSAL FUNGUS. 



Rose canker is produced by the parasitic growth of a fungus, Cylin- 

 drocladium scoparium Morg., within the tissues of the host (rose plant). 

 Previous to 1917 this fungus had not been reported as a parasite. It was 

 first found in Ohio by Morgan (1892) growing on an old pod of the honey 

 locust {Gledilsia triacanthus L.). Seven years later it was reported again 

 by EUis and Everhart (1900) as growing on dead leaves of the papaw 

 tree {Asimina triloba Dunal), and described as a new species, Diplocladium 

 cyUndrosporum E. and E.; but a study of the type materials of the two 

 species by Massey showed them to be the same. As far as the literature 

 shows, these are the only times that the organism had been observed up 

 to 1916, and both times as a saprophyte. 



The body of the fungus is composed of (1) mycelium, (2) sclerotia, 

 (3) sporophores (conidiophores), and (4) spores (conidia). These four 

 parts, or organs, of the fungus are here described separately. 



Mycelium. 



The mycelium is the part of the parasite which lives inside the tissues 

 of the rose stem. It is composed of many microscopically slender, branch- 

 ing, tubular threads (hyphse) which grow in every direction through the 

 host cells for the purpose of securing nourishment from them for the 

 fungus. Incidentally, in this process, the cells are killed and turn brown, 

 thus producing the canker. The hyphje are 4 to 6 « in diameter, and are 

 divided by cross-walls (septa) into cells 5 to 20 times as long as their 



