jan. i 3 , i 923 Forcing the Germination of Freshly Harvested Wheat 95 
DISCUSSION 
The work reported in this paper does not warrant an attempt to discuss 
in any detail the processes involved in after-ripening of the cereals or the 
numerous hypotheses previously offered to explain either these processes 
or the unanalyzed fact of after-ripening. Previous work by others has 
been cited when it was sufficiently related to the work herein reported. 
The enzymic theory of after-ripening has been almost entirely neglected 
in the references to the literature, not because this theory does not 
deserve mention but because the investigation did not touch on that 
phase of the general problem. The principal aim has been to present 
the results which are of value in the practise of seed testing and to fortify 
these results by citations of the results of others rather than to illumine 
or to explain the physiology of after-ripening or of germination. 
All of the treatments which were of value in increasing the germination 
of the incompletely after-ripened cereals may logically be considered in 
connection with their oxygen and water requirements if we consider the 
effect of dry heating to be to increase the permeability of coat structures 
to oxygen. But there is no proof that heating has this effect. It may 
act in a more direct way on the embryo. In like manner in the other 
beneficial treatments effects upon the embryo protoplasm are not always 
out of the question. The bulk of the evidence does, however, seem to 
favor an explanation in which oxygen and water relations are involved 
and coat effects are important. Oxygen relations appear to be especially 
important. Since the cereals investigated seem under any conditions to 
absorb much more water during the germination test than the minimum 
required for their germination and since increased oxygen forced germina¬ 
tion it seems probable that moisture and imbibition effects were related 
to the effects upon oxygen relations and respiration. Since the grain 
can be forced to germination and vigorous growth at any time, it does not 
seem that a storage of oxygen is a necessary part of after-ripening as 
postulated by Hoffman (23 ). The more probable explanation is that the 
treatments which force germination merely bring about the necessary 
increase in oxygen supply by removing coat structures or increasing their 
permeability to oxygen and that this change in permeability of the coat 
occurs also in normal after-ripening. Kiessling’s (28) results with heating, 
with and without loss of moisture and in atmospheres of various compo¬ 
sitions, upon which his stimulus hypothesis of the effect of heating is 
based are at least as readily explained on the basis of coat permeabilities. 
This is the situation which Atwood (7) found with wild oats, but it does 
not hold good for rice with which there must be either a storage of oxygen 
or a decrease in oxygen requirements during after-ripening. 
Windisch ( 44 ), neglecting coat factors, lays emphasis on cell-wall 
permeability factors within the grain, which influence osmotic move¬ 
ments of nutrients. Windisch’s hypothesis is not in consonance with 
the ready germination of the fresh grain when coat structures are 
removed or weakened. 
The interrelations between moisture content, temperature, coat char¬ 
acteristics and changes therein, oxygen intake, rate of imbibition, rate 
and character of respiratory exchanges, response of the protoplasm to 
wounding and to the other treatments, changes in food reserves, the 
formation and activation of enzyms during the period of after-ripening 
and under both normal and forced germination ought to be thoroughly 
investigated, as well as the effects of the different treatments so far as 
