120 
WM. CROCKER 
or more of the processes preceding or accompanying germination. 
The problems are becoming questions of the conditions for growth of 
the embryo and the fundamental changes occurring in the embryo 
with the beginnings of germination on one hand : and a study of the 
physical characters (permeability and breaking strength) of the 
colloids of the seed coats as affected by aging, various conditions and 
reagents, upon the other. 
2. Seed coats have a surprisingly important role to play in both 
primary and secondary dormancy. Often they are of such colloidal 
nature as to be modified by even very low concentrations of a variety 
of reagents thus permitting the growth of the embryo. In the past 
such results have been interpreted frequently and wrongly as stimulus 
responses. 
3. Regarding conditions for germination of seeds, the recent trend 
is toward the need of certain general physical conditions and away 
from the need of specific chemical stimuli, or even chemical stimuli at 
all. The same change in view is occurring in reference to germination 
of pollen. ^2 We apparently have here a generalized physiology in 
contrast to the situation in the organs of more highly differentiated 
organisms. In mammals for instance dormancy of an organ as well as 
its rate and course of development are often determined by specific 
substances from the great number of highly specialized glands. Even 
if Kidd's conclusion is correct, that carbon dioxide often produces 
dormancy by narcotizing seeds, we have the action of a general 
product of metabolism rather than a specific material. 
4. After-ripening of seeds, or the changes occurring during dor- 
mancy and finally making germination possible, may involve growth 
of a rudimentary embryo, fundamental chemical changes in an other- 
wise mature embryo, or chemical changes in the coats. In after- 
ripening there is often a complex interrelation between coat and 
embryo changes. 
5. Problems in dormancy lend themselves beautifully to the 
mechanistic attack. 
6. Finally, I must state that the dominantly mechanistic interpre- 
tation I have given dormancy in seeds is not that held by all or perhaps 
even a majority of the workers in this field; but this viewpoint has re- 
cently made great advances possible and promises much for the future. 
University of Chicago 
Tokugawa. Journ. Coll. Sci. Tokyo, 35: I. 1914. 
^2 Martin. Bot. Gaz. 56: 112. 1913. 
