4 _i6 Horne and Williamson .— The Morphology and 
(c) The growth-rate in all concentrations is considerably greater than 
it is in the controls (pH 7-4). 
E. viridescens (Fig. 15). 
[a) The optimum growth takes place in the o*i per cent, concentration 
(hydrogen-ion concentration less than pH 3). 
( b ) The growth-rate increases progressively when passing from the 2 to 
o-i per cent, concentration. 
(e) The growth-rate is greater than it is in the control in all except 
the 2 per cent, concentration. 
Fig. 15. E. viridescens. Growth on potato extract agar with various concentrations of malic acid. 
II. Tartaric acid (Figs. 16 and 17) 2 per cent. = pH 2*4; 0-25 per cent. = 
P H 3 - 
E. catemdata (Fig. 16). 
(a) The optimum growth occurs in the 1 per cent, concentration. 
(b) The order of progressive decrease in the growth-rate is as follows : 
1, 2, 0-5, and o-i per cent. 
( c ) The growth-rate is greater than it is in the controls in all concen¬ 
trations. 
( d) The curves illustrating growth in the 1, 0-5, and o-i per cent, con¬ 
centrations bend after the eighth day. As growth proceeds, 
both the acid concentration and the hydrogen-ion concentration 
of the media will be lowered, owing to the evolution of ammonia 
through the digestion of protein present in the potato extract, 
in addition to the lowering caused through utilization of acid. 
