276 



Journal of Agricultural Research 



Vol. XIII, No. 5 



partment on wire hammocks. Each compartment was provided with a 

 short thermometer which could be read through the glass top. The tem- 

 peratures and percentage of germination are recorded in Table III. 



Table III. — Relation of heat to the germination of spores of Marssonina panattoniana: 

 Test with hanging-drop cultures in a differential thermostat 



Time. 



First trial: 



12 noon 



5P-m 



6 p. m 



8 p. m 



Percentage of ger- 

 mination 



Second trial : 



12 noon 



2 p. m 



8 p. m 



Percentage of ger- 

 mination 



Temperature in compartments. 



"C. 

 60 

 60 

 60 

 60 



° c. 



49- 5 



45 

 44 

 43 



43 

 44 

 44 



III. IV. V. VI. VII. VIII. IX 



° C. 

 37 

 35 

 33-5 

 33 



37 



37-5 



37 



c. 



34 

 32 

 29 

 28 



32 

 31 

 30 



"C. 



28 



24-5 

 24- 5 

 24 



66.66 



27 

 24 

 24 



85 



"C. 



22. 5 

 20 

 20 

 19-5 



50 



21. 5 



20 



20 



54 



c. 



15- 

 IS- 

 15 



15 



16 

 15 



IS 



II- 5 



10-5 

 10-5 



30 



It is readily seen that the fungus does not develop in even moderately 

 high temperatures. This is consistent with the behavior of the fungus 

 in the field and in other laboratory experiments. 



THERMAL DEATH POINT OF SPORES 



A Spore suspension was prepared from a fresh culture and drawn up 

 into capillary glass tubes which were sealed at both ends by flaming in a 

 Meeker burner.^ These were subjected to various constant temperatures 

 in water baths for 10 minutes and then "shot" into test tubes of melted 

 agar by breaking one end and applying a flame to the other end, after 

 which plates were poured. The results are given in Table IV, 



Table IV. — Determination of thermal death point of spores of Marssonina panattoniana 



in capillary tubes 



1 Novy method (Levin, Ezra. THE LEAF spot disease op tomato. Mich. Agr. Exp. Sta. Tech. Bui. 



25, p. 21, I916). 



