414 
Horne and Williamson .— The Morphology and 
Growth in diameter {cm.) of E. viridescens on agar containing 
tannic acid in different concentrations. 
Concentrations. Interval in days. 
4 
. 5 
6 
7 
9 
10 
2.0-0.5 
nil 
nil 
nil 
nil 
nil 
nil 
0-25 
o -35 
o -35 
0.4 
0.4 
o -5 
°*5 
O-I 
0.25 
o -5 
0.85 
i -3 
i*8 
2 -3 
C. 1 
2.05 
4.2 
5-85 
7-65 
10.6 
>11.0 
C. 2 
2.1 
4*35 
6.15 
8-i 
10.5 
>11-0 
Growth occurred only in cultures containing 0-25 and o-i per cent, acid 
with appreciable growth only in the 1 per cent, concentration, but consider¬ 
ably less than that in the control plates. 
From observations made of growth in other media with a similar pH 
value, the hydrogen-ion factor should not cause growth retardation to this 
extent. Hence the check to growth must be ascribed to some other factor. 
Growth in diameter (cm.) of E. catenulata and E. viridescens on agar 
containing gallic acid in different concentrations. 
Concentrations. 
Interval in days. 
4 
5 
6 
by 
/ 
9 
10 
I. 
E. catenulata. 
2-0 
0-2 
0.5 
o-8 
1.05 
i-6 
I *95 
T, 5 
o-3 
0-9 
1-2 
i*6 
2.4 
2.9 
1.0 
0.65 
i-3 
i-7 
2.2 
3-3 
3*8 
o-5 
o*8 
i*45 
2-0 
f 
2*6 
3-9 
4*55 
0.25 
0.85 
I *55 
2*2 
2.7 
4.0 
4*^5 
O-I 
o-8 
i-55 
i-95 
2.7 
3-85 
4-5 
C. 1 
°*55 
1-05 
I# 45 
1.9 
2-55 
3-05 
C. 2 
o-6 
1.1 
i -4 
1.8 
2-5 
2.95 
II. 
E. viridescens. 
2.0—1 >0 
nil 
nil 
nil 
nil 
nil 
nil 
c-5 
o*6 
0-9 XM 
i*4 x 1-7 
2.8 x 3-0 
5.9 x 6-o 
7-ox 7.5 
0.25 
I *2 
2-7 x 2-9 
4-6 x 4.7 
6.3x67 
>io«o 
>10-0 
O-I 
i*7 
3.6 
5-6 
7-3 x 7-5 
>10.0 
>10-0 
C. 1 
2.05 
4-2 
5-85 
7-65 
io-6 
>11-0 
C. 2 
2-1 
4-35 
6.15 
8.1 
10.5 
>11-0 
N.B. The pH values of the gallic agars were as follows : 2 % = pH 3.1 ; 1 % = pH 3.2 ; 
o-i % = pH 3.8. 
The following are the chief points of interest : 
I. E. catenulata . 
(a) The total growth at the end of ten days exceeds that in the con¬ 
trols (agar alone) in all except the 2 and 1-5 per cent, members 
of the series. 
(b) Increase in the rate of growth occurs when passing from the 2 to 0-5 
per cent, concentration. 
II. E. viridescens. 
(a) No growth occurred in 2, 1-5, and 1 per cent, gallic agars. 
