342 
Journal of Agricultural Research 
Vol. II, No. s 
terial contaminations (not the molds) can be almost entirely eliminated 
without injury to the spores by treating with copper sulphate (see 
p. 356 - 357 )- 
The isolation of the organism gave excellent opportunity for a closer 
study of its relation to various media and temperatures. Plate XXXIV, 
fig. 1, shows its growth in about six weeks from transfer on carrot agar 
at 20 0 to 23°, 30°, 35°, and 40° C., respectively. At 40° there is no 
growth. At 35 0 the growth is very slight, light brown in color, and 
much attenuated. A culture at 32.5 0 C. grew poorly, and those at 
higher temperatures were eventually killed, for they did not grow on 
being removed from the incubator. The rapid development at 30° 
indicates that this is very near the optimum temperature for the organism, 
and this is borne out by the studies of germination given in Table I. 
Table I .—Germination of spores of the head-smut organism at various temperatures 
Serial No. 
Date of test. 
Tempera¬ 
ture. 
Duration 
of test. 
Germina¬ 
tion. 
1912. 
•c. 
Days . 
Per cent . 
1 
Dec. 16 
29-31 
3 
6. 0 
2 
.. .do__ 
a 20-2I 
3 
2. 0 
3 
.. .do. 
16-20, 
2 
. 2 
4 
...do. 
3 
• 2± 
5 
...do. 
i 4-5 
3 
0 
6 
...do. 
12 
3 
O 
7 
...do. 
8-5 
3 
O 
8 
... .do. 
7-5 
3 
O 
9 
...do. 
4 
3 
0 
10 
...do. 
1 
3 
0 
1913- 
11 
Jan. 8 
40 
3 
0 
12 
...do. 
37 - S 
3 
0 
13 
...do. 
35 
3 
0 
14 
...do. 
32. 5 
3 
i -5 
I S 
...do. 
30 
3 
7-9 
16 
...do. 
“23-25 
3 
3 -o 
17 
...do. 
<*20-23 
3 
1. 0 
18 
...do. 
18-20 
3 
2. 0 
19 
...do. 
20-23 
3 
5 -o 
20 
Mar. 18 
27 
8 
4.0 
21 
.. .do. 
17 
8 
•4 
22 
...do. 
0 
8 
0 
2 3 
...do. 
23 
8 
2.0+ 
24 
Mar. 19 
27 
7 
13 - 1 
25 
...do. 
17 
7 
1. 0 
<* All but these were incubated in the dark. 
These germinations were made in carrot-agar plates with material 
collected at Amarillo, Tex., in September, 1911, from Red Amber sorgo, 
except the last two, which were from kafir grown in 1912. From Nos. 11 
to 19, inclusive, the number of spores counted in each case was 200; 
for the rest of the tests the count was not recorded except as follows: 
No. 20, 1,000; No. 23, 500; No. 24, 541; and No. 25, 818. 
