June 5, 1916 Silver-Scurf of Irish Potato 343 



conidia germinated within 48 hours, and pieces of the mycelium in the 

 cultures also showed growth. Agar culture and cultures on sweet-clover 

 stems subjected to the same temperature also remained viable, as indi- 

 cated by subsequent transfers, hanging-drop cultures showing that both 

 conidia and mycelium retained their vitality. 



In the test with naturally infected and artificially inoculated potatoes 

 sporulation occurred on the former at temperatures ranging from 6° to 

 27° and on the latter at a range of from 1 2° to 27° C. In cultures on agar 

 media and sweet-clover stems subjected to 35° and 50° further growth 

 was inhibited at the former temperature, but the fungus remained alive 

 after two weeks' exposure, while it was killed when subjected to 50° for 

 three days. 



REACTION OF THE FUNGUS TO MEDIA 



Since 5. atromrcns is a relatively slow-growing organism, tests were 

 made with media of different grades of acidity with a view of facilitating 

 growth in culture. The media used for this purpose were synthetic, 

 Lima-bean, string-bean, oat, potato, corn-meal, and beef agar, all of 

 which varied in reaction from -f 15 to — 15 Fuller's scale. 



Two plates each of these media equally diluted with conidia from the 

 same culture were poured, and all were incubated at room temperature. 

 Examinations of the colony development, including nature and extent of 

 growth and sporulation, were made at 4-, 6-, and 12-day intervals and 

 showed that 5. atrovirens developed slightly faster on potato and Lima- 

 bean agar than on string-bean, corn-meal, or oat agar; that growth was 

 much retarded on beef agar; that mycelial development was very de 

 cidedly inhibited on S3^nthetic agar; that sporulation occurred slightly 

 sooner on oat agar than on the other agars; and that the hyphae on 

 fruiting remained lighter in color on Lima-bean and beef agars than on 

 other agars. 



The optimum reaction appeared to depend largely on the kind of 

 medium. On potato agar no perceptible difference in growth appeared 

 between -f 10 and — 10, but mycelial development was much retarded at 

 -1- 15. On corn-meal agar only -j- 1, o, — i, —3, —5, and — 15 reactions 

 v/ere run, because of the fact that hydrolysis took place when there was a 

 higher degree of acidity. In this series -f i reaction was the optimum 

 for growth, and in this case the mycelium became dark earlier than was 

 the case in the minus reactions, owing possibly to the hydrolytic action 

 of the acid on the media. On Lima-bean agar with -f 5 to — 3 reactions 

 the apparent growth of the fungus was not much changed, but with 5 to 

 10 and —3 to —10 reactions mycelial growth was perceptibly retarded. 

 On beef agar optimum reactions ranged from o to +1, very little differ- 

 ence appeared in the colonies at -f 3 to — 3, growth was gradually retarded 

 at 5 to 15, and no colonies were macroscopically visible at the end of 10 

 days on reactions ranging from — 5 to — 15. 



