262 Report of the Department of Botany of the 



ture accompanied by rain, preferably gentle rain, followed by mist 

 and fog. The rain is essential for the discharge and distribution 

 of the spores, but gentle rain and fog are more favorable 

 for the lodgment of the spore in a single place where it maj' 

 germinate. No difficulty has ever been experienced in bringing 

 about germination at various temperatures so that the low temper- 

 ature usually attendant on infection periods doubtless should be 

 regarded as an incidental meteorological condition. The low tem- 

 perature actually retards the germination of the spores and thus aids 

 in reducing the amount of infection. 



Period of incubation. — After the germ tube of the spore effects 

 an entrance into the interior a considerable period of time elapses 

 before a lesion is apparent. Gregory (1913) records a period of 

 incubation of about 30 days. Inoculations on the green shoots of 

 vines in the greenhouse by Gregory, using a strain isolated from 

 fruit, gave lesions in about a month. Also inoculations of shoots 

 in the greenhouse with spores from a culture kept pure for four years 

 gave lesions in approximately the same length of time. In 1908 

 when infection was supposed to have occurred on May 28th, lesions 

 were found abundantly on June 26th. In 1909 infection probably 

 occurred on May 28th, while lesions were found abundantly on July 

 1st. Possibly a search for these a few days' earlier would have revealed 

 their presence. In 1912, when infection occurred on May 28th 4 and 

 29th, unusually abundant infections were apparent on July 3d. How 

 much earlier than this date they appeared is not known. Finally, 

 the writer, as recorded later, inoculated young shoots on May 21, 

 1913, and found the first well-developed lesions June 23d. It would 

 seem then that approximately 30 days are required before the lesions 

 caused by the fungus are evident. 



For the most part only a single period of infection occurs in any 

 given year. This is evident from the fact that the lesions appear 

 almost entirely at the base of the shoots, usually between the first 

 three internodes. It is possible that the tissue of the host is not 

 susceptible after a certain period, as in the case of the black-rot 

 fungus. The more plausible explanation, however, would be that 

 the spores were all matured and discharged at about the same time. 

 For the most part it is impossible to find pycnidia with spores after 



4 It is only a coincidence that prolonged periods of rain and fog should have occurred 

 three different years on this date. 



