138 INTERNATIONAL CONGRESS OP VITICULTURE 



that germination by means of the germ-tube occurs only in moist air. 

 The writer has never observed this type. In the great majority of cases 

 zoospores are formed. Very rarely the entire contents of the conidium 

 emerges, forms a wall about itself, and eventually produces a tube. 



In one case a number of conidia were observed which produced several 

 amoeba-like bodies, emerging in each case from the apical end of the 

 conidium. After a short period, during which they moved about in the 

 typical amoeba-like manner, they came to rest and became globose as do 

 the zoospores. 



According to Viala (1893), the optimum temperature for germination is 

 from 28 to 30 C. At this temperature the zoospores are produced in about 

 one-half hour. At temperatures from 10 to 17 C., germination only occurs 

 after two or three days and a temperature of 2 to 5 C., prevented germina- 

 tion entirely. Istvanffi (1913), on the other hand, states that the optimum 

 temperature for germination is from 20 to 22 C., while at 28 to 30 C. 

 germination practically ceases, being feeble at the end of six to ten hours. 

 He found that after two or three hours there is profuse germination at a 

 temperature of 14 to 15 becoming slight at 8 C. Melhus (1911) states 

 that a temperature of 10 C: is most favorable to conidial germination. 



During the summer of 1912 numerous attempts were made to germinate 

 the conidia at room temperatures, 70 to 80 F., and often as high as 

 90 F. In some cases there was absolutely no germination after two or 

 three days. All variety of condition were given except to change the 

 temperature because at this time facilities were lacking for that type of 

 experiment. 



In 1913 an ice-box was used in which a temperature of 50 F. easily 

 could be maintained. At this temperature fully 95 per cent germination 

 was always obtained in two to six hours, averaging about three hours. At 

 70 F. only 40 to 50 per cent of the conidia germinated, in about one-third of 

 the time, however, while at 80 to 90 F. there was no germination. When 

 the slides holding the spore-laden drops were placed directly upon the ice, 

 thus obtaining a temperature of 35 to 41 F., a slight germination by means 

 of zoospores occurred in about twenty-four hours. Another point which 

 was observed concerning the spores maintained at low temperature is that 

 the zoospores continue active for a much longer time than at the higher 

 temperatures. In the latter case the writer (1913) has found that it is com- 

 mon for them to rest in about thirty minutes and to have completely germi- 

 nated in three to twelve hours. In the former, the zoospores are still active 

 from twenty-four to thirty hours after germination. In the opinion of the 

 writer the optimum temperature for germination lies between 50 and 60 F. 



Speaking of the effect of light upon the conidia Cuboni (1889:33) says: 

 "the conidia which have been exposed to an intense light for some time, 

 according to my observations, are sterilized and unable to germinate." 

 Istvanffl (1913) makes a similar statement to the effect that conidia placed 

 in water in the morning and maintained in obscure illumination germinate 

 during the afternoon while those which were placed in strong light did not 

 germinate until the following morning. Melhus (1911) states, however, that 

 if the temperature is low, light will have no effect on germination. 



In this connection the writer has conducted experiments and made 

 certain observations. Conidia were placed on ice in a glass chamber and 



