640 ' STATE BOARD OF AGRICULTURE. 



This set of phenomena indicated that the initial attack of the fungus pro- 

 duces little effect on the host, and it is only after several days that the 

 fungus, probably by its by-products kills the tissues. While no work 

 has been done with the by-products of this fungus, it may be mentioned 

 that coincident with the killing of the host tissue occurs the darkening 

 of the tomato agar. Experimentation with such products would 

 undoubtedly yield results, opening up a practically untouched field of 

 Plant Pathology. 



The Subsequent Development: 



On the sixth day submerged pycnidia could be seen in the inoculated 

 leaf. The record with media was similar. On the eighth day the 

 pycnidia were erumpent. Sections at this time showed that spore for- 

 mation was beginning. On the thirteenth day exudation of spores oc- 

 curred and this was taken as an indication of maturity of the spores. 

 The record with media paralleled this with the exception that the spore 

 exudations were more extensive in the moist test tube. 



Infection and Moisture: 



In the experiments so far reported in testing the pathogenicity of the 

 fungus the inoculated plants were left in the moist chamber — sometimes 

 in a chamber filled with a fine spray — for a comparatively long period. 

 Experiments were later inaugurated to find the approximate number 

 of hours requisite in the moist chamber to insure infection. 



Previous experiments had shown that 100% infection followed the 

 placing of viable spores on the under side of leaves. The flecks of cotton 

 were found valuable as a marker and as a device for preventing the wash- 

 ing of the spores from leaf to leaf. Five leaflets each of ten strong vigor- 

 ous plants about 7-14 inches tall were inoculated with spores from the 

 stock pure culture. Nine^ of these plants were put in the Wardian case 

 which was provided with a jet of water which struck the top and broke 

 into a fine spray. A plant was taken out at intervals of 6, 12, 24, 36, 48, 

 54, 60, and 72 hours after inoculation. Each plant was immediately 

 dried by the breeze from an electric fan. After an interval of 15 minutes 

 these plants were placed on a shelf in the window of the laboratory. 

 After five days all plants showed typical spots on the inoculated leaves. 

 The other leaves were healthy. That plant which had not been put into 

 the moist chamber showed as typical a case of infection as the others. 

 This experiment is in striking variance to the usual experience with 

 plant pathogenes, since it is commonly stated that the .host must be wet 

 for a number of hours at least in order for infection to occur. 



On account of this contradiction the experiment was immediately re- 

 peated with exactly similar results. The technique of the two experi- 

 ments was alike with the exception that in the second experiment the 

 plants were kept in the blast of the fan, following removal from the 

 moist chamber, until infection was evident. No variation from the nor- 

 mal time was observed. 



An experiment was then performed in which six small plants fresh 

 from the greenhouse were inoculated respectively on the upper and lower 

 leaf surfaces with a loop of spore suspension. The atmosphere in the 

 greenhouse was such that the plants were in a condition of incipient wilt- 

 ing and the water drop disappeared at once. (August, 1914). These 



'One plant was not put into the moist chamber. 



