EXPERIMENT STATION BULLETINS. 



587 



These results show that minimum temperature for growth is close to the 

 freezing point of water; maximum temperature is around 28°C. Optimum 

 temperature is somewhere in the range of 16 to 20 °C., though very good 

 growth is produced with a few degrees variation either way. 



Pycnidium Production — 



Quite often pj'cnidia are not produced on a solid medium and when they 

 do make their appearance it is usually in old cultures where there is great 

 difficulty in making estimates for comparison of response to diiferent treat- 

 ments. 



Cultures of the organism on filter paper, prepared as described by Coons*, 

 are more satisfactory for determining the value of various factors, in pycnid- 

 ium production. Fruiting bodies have been found to be formed in greater 

 numbers and results are more easily and accurately estimated. This method 

 consists, essentially, in placing filter paper cones in a deep culture dish with 

 the addition of a liquid medium. The nutrient solution used has been either 

 cornmeal broth or Coons' s>Tithetic solution. Either is very satisfactory 

 although the latter gives a greater mycelial development and a larger num- 

 ber of pycnidia. 



Four deep culture dishes, prepared as outlined above, were inoculated 

 with mycelium of Phoma apiicola and placed in each compartment of the 

 differential thermostat. They were allowed to remain thirty days. During 

 this period, the temperature in the basement in which the test was conduct- 

 ed, was fortunately very constant. Therefore, the temperature in the dif- 

 ferent compartments varied little, after the first two days. The tempera- 

 tures given below are averages for the period; except in the case of the last 

 two figures the variation was not more than one degree in either direction. 



TABLE 3. — THE EFFECT OF TEMPERATURE ON PYCNIDIUM FORMATION. 



The quantity of mycelium produced at different temperatures is in har- 

 mony with previous experiments. Color reactions on different media have 

 been noted before, but they came in here in a very pronounced form in re- 

 sponse to heat. At 4° and 10°, the mycelium was almost white. As the 

 temperature increased, the color became more intense. At 26° there was 

 very little vegetative growth, but that which was produced had a very in- 

 tense, dark bluish cast. 



* Coons, G. H. Factors Involved in the growth and pycnidium formation of Plenodomus fuscomacu- 

 lans. Jour. Agr. Res. 5:713-769. 1916. 



