MECHANICS OF DORMANCY IN SEEDS 
117 
tions on one hand or a slow process of decay of the coats themselves 
on the other. This gives seeds ready for germination at every break 
in vegetation — a matter of great importance in the struggle among 
plants. Induction of dormancy in seeds capable of germination also 
throws much light upon a phenomenon very common in nature — the 
primary dormancy taken on by seeds of non-viviparous plants with 
the approach of ripening. As Guppy and Kidd have emphasized, 
vivipary is generally connected with absence of seed coats or with 
poorly developed ones. Well-developed coats play a dominant part 
in primary as well as in secondary dormancy; on the other hand we 
have already shown that primary dormancy is sometimes due in the 
main to the embryo and is only lengthened by the coats. 
Forcing Agents 
The effect of forcing agents upon dormant seeds is a topic deserving 
much attention, but time will compel us to limit it to a few general 
statements. Already a number of references have been made to 
certain forcing agents. 
Acids and bases are frequently found effective through a physical 
or chemical modification of the colloids of the coats, while in the haw 
acids apparently force germination by changing the reaction of the 
embryo. 
Freezing or freezing and thawing"' are means of forcing and 
probably are of very great significance in nature. In general the 
work in this line has not been directed at the mechanism involved and 
throws little light upon the part of the seed effectively modified as well 
as the nature of the modification. Low temperature, but not freezing 
or freezing and thawing, hastens the after-ripening in the embryo of 
Crataegus. Evidence indicates, however, that the beneficial effects 
of freezing are often through coat changes. 
The forcing action of salts"' is frequently reported, but here 
again the studies are not directed at the mechanism involved, although 
many writers make the gratuitous assumption that their effects are 
nutritive or stimulative to the embryo. They will have to meet the 
rather general existence of non-living semi-permeable coat membranes 
that permit little or no entrance of salts. It may be found that salts 
are often effective through a modification of the colloids of seed coats. 
Kinzel. Frost und Licht als beeinflussende Krafte bei der Samenkeimung. 
Ulmer, Stuttgart, 1913. 
Pammel and Lummis. Proc. Soc. Prom. Agr. Sci. 24: 89. 1903. 
