Physiology of the Genus E id ami a. 421 
(c) The growth-rate is greater than it is in the control in the o*i per 
cent, concentration after the seventh day. 
Tannic acid, in the concentrations used, appears to have little effect on 
growth in the case of E. catenulata , but with E. viridescens an increase 
beyond o-i per cent, exercises a strongly retarding influence, the retardation 
being more pronounced than that exercised by gallic acid. Although 
E. viridescens exhibits these striking growth differences, the hydrogen-ion 
concentration of the tannic acid cultures (pH 4-4-4) is approximately the 
same, and not inimical to growth (see E. viridescens , malic acid). Again, 
with E. catenulata the growth-rate is very different in o*i per cent, gallic 
acid and tannic acid respectively, where the hydrogen-ion concentration lies 
between similar limits. 
F. Growth in Equimolar Solutions of Organic Acids. 
In order to assist in interpreting the experimental results obtained 
through growing the species of Eidamia in media containing organic acid 
in percentage concentration, some preliminary experiments were set up, 
using a series of media with certain acids in equimolar proportions. For 
this purpose potato extract agar was prepared, containing N/50 citric, 
malic, tartaric, and gallic acids. Four lots of ico c.c. acid-containing media 
were prepared, using 80 c.c. of potato extract agar, and 20 c.c. of distilled 
water containing (a) 0*268 grm. of malic acid, (b) 0-3 grm. of tartaric acid, 
(e) 0*384 grm. of citric acid, and (d) 0*34 grm. of gallic acid respectively. 
The potato extract agar and the acid solutions were autoclaved separately, 
and the latter added to the extract afterwards. The pH values of the 
