Physiology of the Genus E id ami a. 41 7 
This change would produce progressive growth retardation, as 
the concentration falls away from that favoured by the fungus. 
Indications of this effect occur, according to expectation, first in 
the o-i and 0-5 per cent, and later in the higher percentage 
concentrations. A similar phenomenon is exhibited with malic 
acid (Fig. 14). 
E. viridescens (Fig. 17). 
(a) The optimum growth occurs at a concentration of o-i per cent, (less 
than pH 3). 
etc l. 
Fig. 16. E. catemilata . Growth on potato extract agar with various strengths of tartaric acid. 
(b) The growth-rate progressively increases when passing from the 2 to 
o-i per cent, concentration, as with malic acid. With the excep¬ 
tion of the o-i per cent, concentration, the growth-rate is less than 
it is in the corresponding malic acid series, and the difference is 
strongly marked in the 1, 1-5, and 2 per cent, concentrations. 
(c) The growth-rate is less than it is in the controls in the 1, 1-5, and 
2 per cent, concentrations. 
(d) The curves do not bend downwards with the lowering of the con¬ 
centration. 
From these results it is clear that tartaric exercises a retarding influence 
on growth, as compared with malic acid, in media containing similar con¬ 
centrations of these acids, the hydrogen-ion concentration being approxi- 
