1170 
Journal of Agricultural Research 
Vol. V, No. as 
From the data in this table it is evident that the amount of carbon 
dioxid evolved in the presence of sugar or clover is far too small to exert 
a marked effect on germinating seeds. 
CALCIUM CARBONATE 
It is well known that free acids greatly retard or prohibit germination 
(3; 4, p. 37). Aside from the direct effect on seeds, an acid reaction may 
favor the growth of injurious micro-organisms. Accordingly, two series 
of tests were made, using a neutral and an acid soil with varying amounts 
of limestone (CaC 0 3 ). The results of the first test are given in Table XII. 
Table XII .—Effect of green clover and calcium carbonate on the germination of 
cottonseed 
No. 
Treatment. 
Germination. 
1 week. 
a weeks. 
3 weeks. 
Relative. 
Per cent. 
Percent . 
Per cent. 
Per cent. 
I 
None... 
*5 
85 
IOO 
2 
1 per cent of clover. 
55 
55 
ss 
64 
3 
1 per cent of clover, 0.1 per cent of calcium 
carbonate.. .. 
35 
40 
4 
1 per cent of clover, 0.2 per cent of calcium 
carbonate. 
15 
*7 
5 
1 per cent of clover, 0.5 per cent of calcium 
carbonate. 
i 5 
17 
6 
1 per cent of clover, 1.0 per cent of calcium 
carbonate.. 
10 
. 
II 
The data show clearly that limestone in concentrations of from 0.1 to 1 
per cent seriously injured the germination of cotton. The seedlings from 
limed soils died during the first or second week. A second test, similar 
to the above, was carried out, using acid soil. Here again calcium car¬ 
bonate seemed to stimulate the injurious factor. 
EFFECT OF HEAT 
The results of previous tests indicate very strongly the biological 
nature of the factor injurious to germination. For example, reduced 
germination is largely associated with the first stages of decomposition. 
Second, the data seem to exclude the possibility of harmful gaseous 
products. It is conceivable that in the early stages of decomposition 
green tissue is favorable to the growth of certain organisms injurious to 
germination. Accordingly, a series of experiments were made in which 
the amount and form of green manure applied, the seed, and the biological 
factors were modified. From 1.5 to 3 per cent of green manure was 
added. To remove the biological factor, the jars and contents were 
sterilized in the autoclave at 15 pounds* pressure for two hours. The 
results of this study were recorded by photographs. Reading from left 
to right (Pi. LXXXIV, fig. 6), the jars were treated as follows: A, none, 
