43 2 CONNECTICUT EXPERIMENT STATION REPORT, IQI2. 



low as 0.2 per cent, in case of var. parasitica, the growth of the 

 fungus causes a darkening of the medium. This indicates an 

 oxidation of the tannic acid by the fungus, since these tubes 

 without the introduction of the fungus remain undarkened 

 except with the higher percentages, when they color as soon as 

 made, upon cooling. With E. gyrosa, this darkening scarcely 

 takes place, and with var. parasitica is less evident in those 

 tubes containing only 0.2 anc| 0.4 per cent, of tannic acid, but 

 shows on all strengths above these with both fungi about the 

 same, though appearing sooner with var. parasitica. 



(2) The medium in the tannic acid tubes remains liquefied 

 when 0.8 per cent, or more tannic acid is added. The acidity 

 of potato- juice agar and, in the lower percentages, of tannic acid 

 potato- juice agar, where darkening of the medium does not 

 interfere, can be tested before and after growth of these fungi 



AT 



by titrating with Na O H, using phenolphthalein as an indi- 

 cator. These tests show that after E. gyrosa or var. parasitica 

 has fully developed in plain potato- juice agar the acidity is 

 practically unchanged; but in tannic acid potato- juice agar both 

 of these fungi cause a lowering in the acidity of the medium, 

 and the higher the acidity usually the greater the loss, though 

 not proportionately greater, as shown by the following tests : 



Tannic Acid Acid Test Acid Test Loss in 



added (per cent.). before inoculation. after growth. Acidity. 



N N 



o.o 0.15 cc. Na O H 0.15 cc. Na O H o.o 



20 20 



0.4 0.5 



0.85 " " " " " 0.35 



1.4 " " " " " 0.7 



1.8 " " " " " 0.9 



(3) Cultures of E. gyrosa var. parasitica containing 0.2, 0.4, 

 0.8 per cent, tannic acid show a more vigorous spore develop- 

 ment than the check cultures of potato- juice agar without tannic 

 acid. The same was true of E. gyrosa regarding mycelial 

 development, but to a less extent, and possibly also as to spore 

 development, though with this fungus the spores do not exude 

 very abundantly in any case. 



(4) At about 4 per cent, the loss in color, especially with E. 

 gyrosa, becomes quite evident. In the liquefied tubes up to 



