Apr. 29, 1918 



Anthracnose of Lettuce 



275 



Tabi,E I. — Growth of Marssonina panattoniana in test tubes on various media 



Medium. 



Prune agar, +30° 



Pear agar 



Nutrient agar . . . 



Parsnip plug 



Carrot plug 



Potato plug 



Glucose agar .... 

 Prune agar, +13° 

 Lettuce agar .... 

 Nutrient agar. . . 

 Corn-meal agar. . 



Com meal 



Oatmeal 



Height 



of 

 growth. 



Mm. 

 1-5 



Density. 



Thick 



Sparse 



Medium . . . 

 Very dense. 



Thick 



Very dense. 



do 



Thick 



Dense 



do 



do 



....do 



....do 



Rate of 

 growth. 



Rapid... 

 , ..do.. .. 

 Medium. 

 ...do... . 

 Rapid... 

 ...do.... 

 Slow. . . . 

 Medium. 

 Rapid . . . 

 Slow .... 

 Medium. 

 Rapid.. . 

 ..do.. .. 



Spore. 



Many. , 

 . . .do. . . 

 Few . . . 

 Many. . 

 Few . . , 

 Many . . 

 Few . . . 

 Many. . 

 ...do... 

 Few . . . 

 Many . . 

 Few . . . 

 ...do. .. 



Chlamydo- 

 spore. 



Produced 



Not produced . 



do 



do 



do 



do 



do 



do 



Produced 



Not produced . 



do 



do 



do 



Color. 



White. 



Do. 

 Yellowish white. 

 White. 



Do. 



Do. 



Do. 



Do. 

 Hvalin. 

 White. 



Do. 

 Pinkish white. 

 White. 



RElvATlON TO EXTERNAL CONDITIONS 

 RELATION TO DESICCATION 



A drop of spore suspension, prepared by filtering a fresh culture 

 through a sterile funnel containing cotton and glass wool, was placed on 

 each of a number of sterile cover glasses and allowed to dry. The cover 

 glasses were then stored in sterile moist chambers. They were removed 

 one at a time at regular intervals, a drop of sterile water was placed on 

 the dried spores, and the cover slip was inverted over a Van Tieghem 

 ring. The spores were found to withstand desiccation for only four or 

 five days (Table II). 



Table II. — Effect of desiccation on the viability of spores of Marssonina panattoniana. 



+ = Germinated ; o=did not germinate. 



RELATION OF GERMINATION TO HEAT 



The relation of spores to heat was determined by placing Van Tieghem 

 cells containing hanging-drops of spore suspension in the compartments 

 of a differential thermostat whose various compartments maintained 

 even temperatures ranging through about 50 degrees. The thermostat 

 consisted of a long galvanized-iron box 5 by 5 by 30 inches, divided 

 transversely into compartments about 2 inches long. At either end was 

 a somewhat larger compartment, one for ice and the other for water 

 heated to 70° C. by means of a carbon-filament incandescent lamp. The 

 box was insulated on the four sides and bottom with ground cork, and 

 on the top with glass. The slides were hung in the center of each com- 



