86 MASSACHUSETTS HORTICULTURAL SOCIETY 



on the parasite warrant the conclusion that, as has been found to 

 be true of many fungi, this fungus is carried through the winter 

 on fallen leaves in which the ascosporic stage develops the following 

 spring. 



Although when mature the asci discharge the spores through an 

 apical pore formed by the rupture of the wall, the spores are 

 apparently not discharged with violence. Wolf states that they 

 merely pile up in a whitish heap in the opened perithecium. How 

 they reach the unfolding leaves of the plant has never been defi- 

 nitely determined, but it is probable that insects, splashing rain, 

 and possible the wind play an important part. Man, in cultivating, 

 may also serve as an agent of inoculation. 



The maturity of the ascospores and the occurrence of rainy 

 periods when the spores are mature are factors governing spore 

 discharge. 



Inoculation. The ascospores which are probably distributed 

 during a rainy period require moisture to germinate and penetrate 

 the host. They germinate within twenty-four hours. Wolf (5) 

 found the period of incubation to be about ten days, small black 

 areas being evident on May 7 from inoculations made on April 27. 



Infection. Infection occurs by the entrance of the germ-tube 

 directly through the cuticle of the leaf. The resulting mycelium 

 remains for some time immediately beneath the cuticle, later 

 penetrating the tissues below, first filling the epidermal cells and 

 only in advanced stages of the disease penetrating the mesophyll. 

 The black appearance of the spots is not due to the fungus, which 

 is almost colorless, but to the disintegration of the cells below the 

 spot. 



Environmental Relations. 



Temperature and especially moisture are factors which may 

 influence the severity of the disease by their effect on the parasite 

 and the host. It is a matter of common observation that green- 

 house roses are more subject to this disease in the spring and 

 autumn when extremes of temperature are most likely to occur. 

 Frequent rains and general cloudiness are important factors at 

 these times. Many growers of indoor roses claim that if the plants 



