420 Horne and Williamson .— The Morphology and 
E. viridescens (Fig. 19). 
(a) The optimum growth occurs at a o-i per cent, concentration. 
(b) The growth-rate progressively decreases when passing from the 
o*i to 2 per cent, concentration. 
(e) The growth-rate is greater than in the control, in all except the 1, 
1 *5, and 2 per cent, concentrations. 
(d) The curves for the 1, 1-5, and 2 per cent, concentrations diverge 
widely ; there is practically no growth in the 2 per cent., although 
the hydrogen-ion concentration is not unfavourable to growth 
(pH 3-4-3-6). In this respect the curves differ from those 
obtained for both species of Eidaniia in the case of malic and 
tartaric acids. 
cm. 
Fig. 20. E . catenulata. Growth on potato extract agar with tannic acid. 
IV. Tannic acid (Figs. 20 and 21) 2, 1, and o-i per cent. = pH 4-4-4. 
E. catenulata (Fig. 20). 
(a) The optimum growth occurs at a 0-5 per cent, concentration, but 
growth at all the other concentrations approximates closely 
to this. 
(b) The growth-rate is least in the 2 per cent, concentration. 
(c) The curve for the control lies midway between those for the 0-5 and 
2 per cent, concentrations. 
E. viridescens (Fig. 21). 
(a) The optimum growth occurs at the o-i per cent, concentration. 
(b) The growth-rate is retarded in concentrations higher than o-i per 
cent., with no growth beyond 0-5 per cent. 
