598 Journal of Agricultural Research voi.xv.no. n 



CULTURAI. CHARACTERS 



The organism was grown on steamed corn meal, corn-meal agar, oat 

 agar, prune agar, and rose canes. Both strains of the fungus grow rap- 

 idly on these media, producing the imperfect stage in three or four days 

 with very little superficial mycelial growth. The pycnidia are developed 

 in great abundance, extruding cinnamon-buff^ spore masses, which often 

 cover the entire surface of the medium. 



Plate 46, D, shows a B culture on rose canes after 22 days' growth, 

 while Plate 46, C and E, reproduces photomicrographs of a similar 

 culture after three months, showing the extruding pycnospore masses 

 and the beaks of the perithecia. Only cultures on rose stems in test- 

 tubes containing a very small amount of moisture and kept approxi- 

 mately at a temperature of 17° C. developed the perfect stage of the 

 fungus. On steamed corn-meal media the superficial mycelial growth 

 was most abundant, appearing pure white at first and soon becoming 

 gray. On prune agar and on corn-meal agar poured plates the culture 

 develops radially from the point of inoculation, concentric rings of the 

 pycnidia appearing at more or less regular intervals. 



LIFE HISTORY OF THE FUNGUS 

 That the life cycle of the fungus may be completed in a comparatively 

 short time is shown from the cultural experiments and from the field ob- 

 servations. From the inoculation experiments it has been shown that 

 infection occurs from both pycnospores and ascospores and that lesions 

 may be produced in from 4 to 15 days. A culture made on February 11 

 from pycnospores produced from stage B had developed the two stages 

 by April 15. On field material collected on March 18 the imperfect stage 

 was present, together with the immature perfect stage. In May spores 

 of both stages germinated in culture, producing the perfect and imper- 

 fect stages as previously described, indicating that a period of rest is not 

 essential for the completion of the life cycle. On the other hand, the 

 spores probably remain viable for a long time, since pycnospores from 

 very thin poured-plate cultures which had dried were viable after having 

 been kept for four months at a temperature of about 17° C. How the 

 fungus overwinters and the manner in which the first infections are pro- 

 duced are still subjects of investigation. It is very probable that the 

 ascospores live over a winter in the old canker and produce the early 

 spring infections. It is not known how the spores are disseminated, 

 whether by wind, rain, insects, or on cultural implements, but it is prob- 

 able that rain plays an important part in distributing the exuded pycno- 

 spores. 



CONTROL MEASURES 



Preliminary experiments in controlling the disease by cutting out and 

 burning the cankered stems have been made, but the results during the 



• RiDGWAY, Robert. C01.0R standards and color nomenclature. .1.3 P-. 53 coL pi. Washington, 

 D. C, 1912. 



