272 Report of the Department of Botany of the 



spraying spores on green parts 



The pathogenicity of the fungus has been established by spraying 

 spores on tender shoots (Gregory, 1913). The writer was not suc- 

 cessful in his earlier attempts to obtain infections in this way. The 

 failures are readily attributed, however, to the fact that inoculations 

 were not made at the most opportune times. Circumstances did not 

 permit trials in the early stages of new growth. Later in the season 

 great difficulty was experienced, both in 1909 and in 1910, in main- 

 taining spore-laden drops of water on the vines for any appreciable 

 length of time. The wind blowing off Lake Erie m the day and 

 towards the lake at night, dried up the moisture before the spores 

 had an opportunity to germinate. The following paragraph copied 

 verbatim from notes written July 10, 1909, gives an idea of the 

 method of making inoculations and the results obtained : 



"An enormous quantity of spores of the dead-arm fungus (3216) 5 

 from pure culture were placed in boiled rainwater in an atomizer 

 and sprayed on all the vines (38) of row two in the experimental 

 block. There had been a heavy rain and even as the spores were 

 being sprayed on (between 8 and 9 p. m.) the rain was falling. So 

 far as I can find no rain fell after ten o'clock. The wind blew while 

 the spores were being applied and presumably all night. The vines 

 are perfectly dry at seven a. m. this morning." 



Similar trials were made in 1909 with various strains of the organ- 

 ism, isolated from different places, on June 22d and 23d, and on July 

 10th, three different trials were made. In 1910 two trials were made 

 on July 12th, one each on August 18th and 31st, and one on Septem- 

 ber 4th. The vines sprayed on August 18th were small and were 

 covered with a bell glass. 



In one case a sprayed row seemed to show an unusual amount 

 of scattering infections, which is not usual, as well as a greater 

 number of infections than neighboring vines. The number of spots 

 was not sufficient, however, to justify the assumption that the 

 spores sprayed on the vines caused the infections, particularly 

 since the presumed period of incubation was not observed nor recorded 

 and cannot therefore be checked against more definite records. 



Inoculations with pure cultures of the fungus (No. 3221, original 

 culture made April 16, 1908) were made May 21, 1913, by suspend- 



6 The figures refer to specimen numbers in the collection of the Department of 

 Plant Pathology, Cornell University. 



