696 Journal of Agricultural Research voi.xx, No. 9 



dense mat over the surface of the culture, its color usually becoming 

 slightly brownish with age. Spore masses often appear above this layer 

 of mycelium. 



On other media. — The growth of the fungus was studied on 25 

 kinds of artificial media, including beef broth agar, corn meal agar, oat 

 agar, apple agar, synthetic agars, vegetable agars, cooked vegetables, and 

 fresh vegetable tissues. The character of growth on the various media 

 used was so uniform and so closely parallel to that on potato agar that a 

 separate description for each is unnecessary. The most noticeable dif- 

 ference was that correlated with the supply of sugar in the medium. 

 Where dextrose was omitted in the formula growth and sporulation were 

 very scanty, and the stromata were few in number and widely scattered. 

 On onion and apple agars made up without dextrose this difference was 

 less marked, probably on account of the presence of a considerable 

 amount of sugar in the plant tissues used. On synthetic agars * with 

 sugar added in the form of maltose, dextrose, lactose, and sucrose 

 copious growth took place with no evidence of preference for any one of the 

 carbohydrates used. Cooked bean pod, onion scale, carrot, potato, and 

 rice supported good development of the organism. On fresh onion and 

 apple, however, the growth was much retarded, and on fresh potato 

 and carrot it was very scanty. Stevens and True (30) report retarded 

 growth on onion broth agar made with red or yellow varieties. The 

 writer has found equally vigorous development on agar made from red, 

 yellow, and white types of onion. 



RELATION OF TEMPERATURE TO GROWTH 



Potato agar plates inoculated with mycelium or conidia of the fungus 

 were kept at temperatures ranging from i° to 35 ° C. The rate of growth 

 was determined by measuring the diameter of the resulting colonies or 

 thalli from day to day. In order to increase the accuracy of the results 

 Petri dishes of equal diameter containing equal amounts of agar were 

 used. In order to overcome the influence of variations in relative 

 humidity prevailing in different incubators the later experiments were 

 modified by placing the Petri dishes in moist chambers first and then 

 exposing them to the desired temperature. It was found after many 

 trials that the best comparative data could be secured at four to six 

 days. The growth was slight at i°, almost negligible at 2 , but an 

 appreciable amount occurred at 8° to io° during a period of 10 to 14 

 days. Above this point the rate of growth increased rapidly, reaching 

 the optimum at about 26 . At 31 to 32 little or no growth occurred 

 on potato agar. The growth at various temperatures on this medium 

 at the end of 6 days is represented graphically in figure 4. 



1 Formula for synthetic agar used: Sugar, ioo gm.; peptone, 20 gm.; ammonium nitrate, 10 gm.; mag- 

 nesium sulphate, 2.5 gm.; potassium nitrate. 5 gm.; acid potassium phosphate, 2.3 gm.; calcium chlorid, 

 0.1 gm.; agar, 20 gm.; neutralized with normal sodium hydroxid. 



