476 
Kidd and West . — The Controlling 
mechanical shock by torsion and pressure. This in itself may be sufficient 
to upset the dormant condition of the embryo, and may account for the 
almost immediate germination of the majority of the embryos employed in 
the above experiments and for the fact that the dormant condition of the 
embryo itself had not been previously discovered in the many experiments 
in which the testa had been completely removed in order to induce 
germination of dormant seeds. 
In the second place, by the removal of the testa, both the entrance 
of oxygen and the escape of carbon dioxide are facilitated. Thirdly, 
a further physical uptake of water occurs after the removal of the testa. 
In the following table the further swelling which occurs in the radicle of 
seeds showing secondary dormancy, after removal of the testa, is indicated. 
It is possible that the tissues are less stable in the fully swollen condition. 
Table XVII. 
Further Uptake of Water by Excised Radicles of Seeds showing Secondary 
Dormancy after Removal of the Testa . 
Time . 
Percentage of 
elongation. 
5 min. 
3*2 % 
11 » 
5 - 2 % 
20 „ 
6.4% 
3 2 „ 
6-4% 
60 „ 
6*4% 
69 >> 
•6-4% 
28 hrs. 
42 °/ o (growth now commenced). 
Before the removal of the testa these seeds were soaked several hours under water. 
Mean temperature of laboratory, I5°C. 
§ 4. Methods of forcing Germination of Brassica alba Seeds 
showing Secondary Dormancy. 
The present section proceeds to experiments dealing with the effect 
of various treatments in forcing the germination of Brassica alba seeds 
showing secondary dormancy. 
Removal or Partial Removal of the Testa . 
It has already been shown that complete removal of the testa induces 
germination ; this fact has been discussed at length in the preceding section. 
It was found, however, in addition, that a considerable percentage of seeds 
germinated immediately after the removal of the outer testa only ; 1 
a similar result was obtained by the removal of a small sector of the testa 
over any part of the embryo. The following table summarizes the results 
of the experiments conducted : 
1 See Appendix. 
