92 
Journal of Agricultural Research v 0 i. xxiii , no. 2 
( 23 ) elaborated a similar hypothesis, so far as oxygen is concerned, to 
explain the after-ripening of cereals. 
On the other hand, Kiessling, in the article just referred to, showed 
that barley after-ripened more slowly in atmospheres in which two- 
thirds of the normal air was replaced by oxygen than in unaltered at¬ 
mospheric air, and also that the beneficial effect of heating, either with 
or without simultaneous drying, was not dependent upon the partial 
pressure of oxygen during the period of heating. Takahashi (41), 
Nagai (57), and Akemine ( 2 ) have all shown that fully after-ripened rice 
germinates and develops considerably in entire or almost entire ab¬ 
sence of oxygen, and Lukas ( 33 ) found that fully after-ripened oats and 
maize, as well as some other seeds, germinated more rapidly in reduced 
air pressure (therefore reduced partial pressure of oxygen) than in 
normal air. The behavior of rice is undoubtedly related to its ecology, 
this grain being adapted for germination under water, as are the seeds 
of many water plants (rj, 14 ). 
From Kiessling’s ( 28 ) and Lukas’s ( 33 ) results, it would seem either 
that the oxygen requirements of the embryos decreased during after¬ 
ripening, or else that increasing permeabilit}^ of the coat structures 
during the after-ripening rendered oxygen in a given partial pressure 
more available for the use of the embryo. Atwood’s (7) results show 
that the latter is probably the case with wild oats, while the work of 
the Japanese workers favors the former explanation with rice. 
In this investigation, increased partial pressures of oxygen were used 
in testing the germination capacity of a number of not after-ripened 
samples of wheat. The apparatus used consisted of a small battery 
jar inverted within a larger battery jar so that two or three litres of 
gas was imprisoned over a water seal. The grain was tested on moist 
blotting paper in open Petri dishes floated on large corks within the 
small inverted battery jars, using 100 grains for each test. Increasing 
the percentage of oxygen in the atmosphere to 36 per cent had appar¬ 
ently the maximum effect on germination. With this percentage 85 
per cent of one sample of wheat germinated in five days against 44 per 
cent with the normal 20 per cent of oxygen, while the amount of growth 
was nearly twice as great. With higher partial pressures of oxygen, the 
percentage of germination was about the same as with 36 per cent, but 
the rate of growth was less. 
WATER CONTENT IN RELATION TO GERMINATION 
Some of the earlier workers on after-ripening of cereals and the effect of 
artificial drying attempted to establish a relation between the moisture 
content of the seeds or alternations therein immediately preceding the 
germination test on the one hand and germination on the other hand. 
As shown in a previous section, artificial drying has usually had a bene¬ 
ficial effect. However, Atwood (7), Kiessling ( 28 ), Kondo ( 30 ) and 
others have shown in articles already cited that after-ripening takes place 
also when loss of water is prevented or even when more water is absorbed 
by the grain during the period of after-ripening. Besides the frequently 
favorable effect of presoaking as well as of drying is opposed to the view 
that the germinating capacity of not after-ripened grain is quantitatively 
related to its water content at the time the germination test is made. The 
relations involved go deeper, are less simple, and involve many other fac¬ 
tors than moisture. 
