418 Home and Williamson .— The Morphology and 
mately similar in each case. Also the two species of Eidamia react very 
differently towards these acids. The hydrogen-ion concentration favouring 
optimum growth is not far removed from pH 2-4 (malic) for E. catenulata , 
and pH 3 (malic) for E. viridescens. In the latter species the region of 
optimum growth does not appear to be sharply marked, and might possibly 
be represented by a curve exhibiting a gentle gradient towards the neutral 
point, but with a steeper descent on the acid side. 
Fig. 17. E. viridescens. Growth on potato extract agar with various concentrations 
of tartaric acid. 
III. Gallic acid (Figs. 18 and 19), 2 per cent. = pH 3*4-3*6 ; 1 per cent. = 
pH 3*4-3*6 ; o*i per cent. = pH 4-2. 
E. catenulata (Fig. 18). 
(a) The optimum growth occurs at 0*5 per cent., but the curves of the 
0-5, o*i, 0*25, and 1 per cent, concentrations approximate 
closely. 
(b) The growth-rate progressively decreases when passing from these to 
a 2 per cent, concentration. 
(c) The growth-rate is greater than it is in the controls, in all except 
the i*5 and 2 per cent, concentrations. 
(d) In this last respect the curves differ from those obtained for malic 
and tartaric acids, but the hydrogen-ion concentration of the 
1*5 and 2 per cent, gallic acid cultures is perhaps less favourable 
to the growth of E. catenulata than that of the corresponding 
malic and tartaric acid series. 
