Ii6 
WM. CROCKER 
counterpart of after-ripening and involves partially reversible changes 
in the colloids of the seed coats in which hysteresis is important. 
Hysteresis is very common in colloids and involves the lagging of 
certain secondary changes behind the primary change that causes 
them. In Amaranthus retroflexus seeds, a month or more of dry 
storage is necessary for after-ripening. The after-ripening seems 
to consist merely in a lowering of the elasticity and breaking strength 
of the colloidsof the coats, rendering the force of the expanding contents 
capable of rupturing them. On the basis of data we need not cite 
here I interpret after-ripening and dormancy production in these 
seeds as follows. Upon drying, the colloids of the coats slowly take on 
new characters which lag a month or more behind the drying and give 
them much lower elasticity and breaking strength when again soaked 
up. This is after-ripening. When soaked up the coats do not imme- 
diately take on that character stipulated by high water content; but 
if the seeds, in a state of saturation, are prevented from breaking the 
coats, the old strength is gradually attained and dormancy secured. 
It is possible that Kidd in white mustard was dealing with hysteretic 
changes involving permeability characters and that carbon dioxide 
was acting merely as an inhibitor to germination allowing these time 
changes to occur rather than acting directly upon the coats as he 
thinks. Undoubtedly other changes in the coat of non-reversible 
type are sometimes involved in producing dormancy. 
While in the cases of induced dormancy, cited above the main 
change is in the coats, these changes act in every case through some 
character of the embryo or other seed or fruit organs — the force with 
which they expand, their capacity to be narcotized by carbon dioxide, 
etc. Conditions inducing dormancy by coat changes must simul- 
taneously bring about important changes in the seed contents; such 
as hydrolysis and condensation of stored foods and enzyme formations. 
These, however, play no role or only a minor role in dormancy induc- 
tion. Finally it is likely that lasting dormancy may be induced in 
which the significant changes are in the embryo. Indeed this is 
assumed to be the general situation by certain workers who are unduly 
imbued with a certain type of ultravitalism that prevents a thorough 
physical and chemical analysis of the problem. 
The biological significance of this secondarily induced dormancy is 
clear. It throws many seeds into a condition of quiescence in nature 
from which they may be aroused only by a marked change in condi- 
