DISEASES OF ROSES 85 



phase in which the fungous Hves during the winter on dead and 

 decaying tissue. 



An examination of the lesions on the leaves during the summer 

 will show the presence of small black pustules which are the fruit- 

 bodies of the fungus. In these fruit-bodies the conidia or summer- 

 spores are born. These spores are matured rapidly during the 

 growing season and are blown about by the wind, thus distributing 

 the fungus and bringing about successive infections with new crops 

 of conidia. This phase of the fungus is the one most commonly 

 met with and has been known under the name of Actinoncma rosae 

 (Lib.) Fries for many years. 



During the winter the sexual or ascigerous phase develops. 

 ^Yhen leaves affected with black-spot fall to the ground during the 

 summer and autumn, the fungus does not die but lives over winter 

 as a normal saprophyte. If examined microscopically during the 

 spring it will be found that another spore-form has developed. In 

 this stage spherical fruit-bodies (perithecia) bearing numerous sacs 

 or asci, each of which contains eight ascospores, are produced in 

 the old leaves lying about on the ground. These fruit-bodies 

 serve to carry the fungus over the winter, the spores being mature 

 at the time of opening of the rose leaves in the spring. 



Inoculation. The old leaves on the ground are to be considered 

 the chief source of primary inoculum in the spring. However, the 

 fungus is carried over winter on plants under glass from which 

 conidia could be carried readily by the wind to the newly develop- 

 ing leaves on out-of-doors plants. Growers frequently buy pot 

 grown plants in the spring to plant in their gardens and are likely 

 to thus carry the fungus to the plants which were out-of-doors 

 during the winter. Scribner (2) who was acquainted only with 

 the asexual stage suggests that the spores (asexual) lodge on the 

 buds in the autumn and remain there dormant until the leaves 

 have expanded the following autumn. In warmer climates the 

 conidia may live over winter and serve as inoculum the following 

 spring. No special investigations on this point have been reported 

 in literature. Wolf (5) could find in wintered material no acervuli 

 which were bearing conidia. It seems very improbable that the 

 conidia winter in any sections of Massachusetts or places having 

 similar temperatures. The evidence derived from observations 



