Influence of Carbon Dioxide . IV. 
477 
Table XVIIL 
Effect of Partial or Complete Removal of the Testa in forcing Germination 
of White Mustard Seeds showing Secondary Dormancy . 
Treatment of 
inhibited seed. 
Not removed to fresh sand. 
Removed to fresh sand. 
Outer testa removed with 
a needle. 
Outer testa rubbed off with 
a towel. 
Both testas removed. 
Portion of the testa over 
the hilum removed. 
Portion of the testa opposite 
the hilum removed. 
Control : new uninhibited 
seeds. 
Percentage of germinated seeds after — 
I 
3 
4 
5 
6 
7 
9 
11 
13 
22 
day. 
days. 
days. 
days. 
days. 
days. 
days. 
days. 
days. 
days. 
0 
4 
4 
4 
4 
12 
12 
1 2 
12 
16 
0 
12 
16 
20 
20 
20 
20 
20 
20 
20 
35 
70 
75 
75 
75 
75 
75 
75 
75 
75 
40 
40 
40 
40 
60 
60 
60 
60 
60 
60 
100 
100 
100 
100 
100 
100 
100 
100 
100 
100 
2 4 
60 
60 
60 
60 
60 
80 
80 
80 
80 
30 
80 
80 
80 
80 
80 
80 
80 
80 
80 
4 
100 
100 
100 
100 
100 
100 
100 
100 
100 
Mean temperature of laboratory, 15° C. 
The seeds which failed to germinate immediately as the result of 
either of these treatments remained dormant for an indefinite period. 
These facts, without being conclusive, indicate that the germinations 
induced result from the mechanical stimulus on the embryo of the treatment 
rather than from any change or weakening in the testa. The experiments 
in which a sector of the testa was removed would seem to rule out the 
factor of mechanical restraint as being operative for those seeds which 
subsequently continued dormant. This factor must have been practically 
reduced to a minimum. 
Re drying . 
It has been shown in a previous paper (1, p. 416) that by redrying 
seeds showing secondary dormancy, the capacity for immediate germina- 
tion is restored. Further investigation during the course of this research 
showed, however, that a time factor is also involved. Thus, a sample of 
twenty-five seeds redried for three days in air at laboratory temperature 
gave only 25 per cent, germination during ten days when reset to 
germinate on wet sand. On the other hand, inhibited seeds redried for 
a month in air at the laboratory temperature gave 100 per cent, germination 
in two days. 
In interpreting these results in view of the fact that no marked change 
in the mechanical resistance of the testa occurs (see Table XV), and ajso 
in view of the fact, which has already been demonstrated, that the seed- 
coats are extremely permeable both to oxygen and to carbon dioxide, we 
conclude that the redrying of the embryo destroys the dormant condition 
K k % 
