96 SEVENTEENTH REPORT. 



These data show that general infection took place in about 4-7 

 days after heavy rains followed by hot weather in mid- August. 

 From reports received from other localities, this seems to have been 

 the critical period throughout Michigan, Indiana, and Wisconsin. 



The fungus can endure a temperature of about 34°C. so that it 

 is not checked by warm weather and is peculiarly severe during hot 

 moist weather. Heavy dews also increase the severity of attack as 

 the vines lie close to the ground and dry out slowly. 



The fact that it grows under such conditions makes its attack 

 most severe where the crop would be the largest, since the host 

 plant is one requiring large quantities of moisture to produce large 

 crops of pickles, the young fruits being 90% water. This fact 

 necessitates a rainy season to make the largest crop. 



Hence where vines are on rather low lands and the humidity is 

 high, we find the fungus damage most serious. One field was noted 

 in 1914 where vines grown on low land made so heavy a growth 

 that the leaves completely covered the surface of the ground and 

 the crop was a large one. 8cab appeared in this field following a 

 heavy rain and hot weather, and a count made a week later, showed 

 95% of the fruit badly infected with the fungus. In this case the 

 hot, moist weather was unusually favorable for the parasite, but it 

 shows how severe it may become, when conditions are favorable for 

 attack. 



INOCULATION EXPERIMENTS. 



These experiments were carried on in the greeuhouj^e with plants 

 which had reached a fair size and were not infected with any 

 fungus so far as known. 



Inoculations were made in tw^o ways as follows : 



1. Spores were sprayed on the plants with a sterile atomizer, 

 spores being in solution in sterile distilled Avater. The plants 

 were all kept under bell jars with a good supply of moisture. 



2. Plants were punctured with a sterile needle after the surface 

 of the plant had been washed with HgCL solution. Spores were 

 introduced into the puncture with another sterile needle and the 

 M'ound covered with a tiny piece of moist cotton, 



Stem Inoculations: 



Stem infection took place in practically all inoculations where 

 I)unctures were made. The stem first showed a water-soaked spot 

 at the point of inoculation after 3 or 4 days. In G days to a week 

 it became a buff brown, and a slight S])litting occurred. However, 



