586 



STATE BOARD OF AGRICULTURE. 



TEMPERATURE RELATIONS. 



Vegetative Growth — 



The seasons of the year, spring and fall, in which this disease is prevalent, 

 suggest a sharp susceptibility on the part of the fungus to high temperatures. 

 This is forcefully brought to one's attention when he attempts to isolate the 

 organism during a hot period, or attempts to grow it in pure culture at a 

 temperature higher than 27 °C. During the summer months it has invari- 

 ably refused to grow in the laboratory, a fact which has previously been 

 noted by Coons (2). Nearly all the cultural work at such times has been 

 done in a basement where the temperature ranged around 21'^C. Where 

 more rapid growth was desired an ice box has been used. This gave a tem- 

 perature of about 16°C. which is very favorable for vegetative growth. 



In the more exact temperature studies with the fungus, a differential ther- 

 mostat, modeled after that of Ganong's, was employed. At one end of this 

 thermostat there was a cubical container which was filled with ice, and at 

 the opposite end, there was a compartment for water which was heated with 

 an electrical immersion heater. A set of chambers made of galvanized sheet 

 iron connected the two compartments. Between the boiUng water at one 

 end, and the ice at the other, there were nine compartments, separated by 

 cardboard partitions. A glass covering was provided to admit light. This 

 gave a range of temperatures which was fairly constant in the middle com- 

 partments, but which was somewhat variable near the two extremes. 



Using this equipment, preliminary experiments were conducted to deter- 

 mine the effect of temperature on quantity of vegetative growth. Test- 

 tube cultures on agar were first used, then, later, in order to get a giant- 

 colony effect for more exact comparison, these were replaced with Erlen- 

 meyer flasks. Twenty cc. of celery agar were placed in each flask; bits of 

 mycelium of Phoma apiicola were placed in the center of the medium and 

 subjected to different temperatiu-es. The experiment, in duplicate, was run 

 for 30 days. The colonies progressed slowly in uniform circles and were 

 actively growing at the time the experiment was concluded. Results in 

 the following table are recorded in terms of average diameter of the colonies. 

 Temperature variations are given as well as the average of twenty readings 

 made during the experiment, values being recorded in terms of the nearest 

 degree. 



TABLE 2. THE EFFECT OF TEMPERATURE ON GROWTH OF MYCELIUM. 



