•588 



STATE BOARD OF AGRICULTURE. 



Pycnidia began to appear at the end of 14 days. Larger number of fruit- 

 ing bodies were produced at 13°, 16° and 18°, though, per unit of myceUum, 

 there were as many produced at 26° as at any other temperature. 



At 4° and 10°, while there was a very good mycehal growth, there were 

 no pycnidia; however, after these cultures were removed and placed at 21° 

 the characteristic bluish color came in and pycnidia were produced as abund- 

 antly as in any of the other cultures. 



High temperature seems to lessen pycnidium production only as it lessens 

 mycelial growth. Low temperature, i. e. below 10°, represses pycnidium 

 production, but a short exposure does not destroy the potentialities for 

 fruiting. 



Grnnination of fipwes — 



In moist chambers and liquid culture, the spores of Phoma apiicola have 

 been very slow in germinating. From 36 to 48 hours have been required 

 for the first indications of germination at room temperature. After the 

 mycelium had shown such a marked response to relatively high tempera- 

 ture, it was suspected that spores were being kept at too high a temperature 

 for the most rapid germination. Pycnidia from deep culture dishes were 

 crushed and the spores placed in small test-tubes containing sterile tap 

 water. These were incubated, four tubes being placed at each temperature 

 recorded below. Loops from these tubes were examined every 12 hours 

 for germination of spores. Results are given in the following table. 



TABLE 4. EFFECT OF TEMI'ERATURE ON GERMINATION OF SPORES. 



At least 24 hours are required for germination at any temperature. The 

 most favorable temperature for vegetative growth, 16° to 18°, is also con- 

 ducive to most rapid spore germination. As indicated by the weak germi- 

 nation at 4°, the minimum is very little below that temperature. Maximum 

 temperature is close to 26°. 



The most outstanding feature is the length of time required for germina- 

 tion even at the most favorable temperature. In this, we probably have a 

 decisive factor making for restriction of the fungus to the underground parts 

 of the host plant under field conditions. The spores, as indicated by in- 

 oculation and germination experiments, require considerable moisture for 

 germination. Under weather conditions which prevail in the celery growing 



