Jan. 20 ,1923 
After-Ripening and Germination of Apple Seeds 
I 57 
for the after-ripening of wild oats, while Kondo (18) has shown that abun¬ 
dant oxygen accelerates the after-ripening of rice, which, when fully 
after-ripened, will, according to Takahashi (, 22 ), germinate in entire 
absence of oxygen. Oxygen has also been shown by Kiessling (16) to 
accelerate after-ripening in cereals under certain conditions, and Hoffman 
(12) has put forth the hypothesis that after-ripening of the cereals con¬ 
sists essentially of a storage of oxygen. Hiltner ( 11 ) and Kiessling (27) 
have also shown, however, that cereals after-ripen, though sometimes 
rather slowly, in closed vessels in almost entire absence of oxygen. If 
free oxygen is essential for after-ripening in this case, the seeds must be 
capable of using it when present in very low partial pressures, and very 
small quantities must suffice. Recent and earlier work by one of us 
(9, 10), as well as Atwood’s work on wild oats, indicated that the embryos 
of the cereals and some other grasses are never essentially dormant, 
the dormancy of the caryopses being imposed by coat structures which, 
in the wild oat at least, limit oxygen supply. Crocker (4) found a 
similar condition in Xanthium seeds. 
The case is different with apple seeds, in which the embryos are dormant 
and require time-consuming changes before they can germinate, even if 
freed from all surrounding structures. But with apple seeds we have 
found very low respiratory quotients at low temperatures which favor 
their after-ripening. There is, therefore, in apple seeds a storage of 
oxygen during after-ripening. Jones (13) has shown that the after¬ 
ripening of the similarly dormant embryos of sugar maple seeds is 
retarded, though not prevented, by inclosing them in desiccators, so that 
oxygen is rapidly replaced by respired carbon dioxid. Recent measure¬ 
ments by Magness (19) show that the concentration of oxygen within 
the core of the apple is not much below that of the surrounding atmos¬ 
phere. The oxygen supply available to the seeds while inclosed within 
the fruit cannot, therefore, be considered physiologically deficient for 
their after-ripening processes, even if these depend upon a much greater 
abundance of oxygen than seems to be necessary for the after-ripening 
of sugar maple seeds. 
EFFECT OF REMOVAL OF THE SEED COATS 
The coverings of the embryos in a mature apple seed consists of: 
(1) A thick, brown, fibrous outer seed coat with open hilum; (2) a thin, 
translucent inner seed coat of very dense structure and without openings; 
and (3) a delicate, whiteish, cellular tissue, somewhat thicker than the 
inner coat, and apparently endospermous. Layer 3 is closely adherent 
to layer 2, and it is impossible to remove the two separately, though the 
embryo is easily bared by removing them together. 
Removal of the outer seed coat has no effect on the germination of 
apple seed previously dry-stored or incubated for a short time at tem¬ 
peratures unfavorable for after-ripening. When the inner seed coats and 
adhering endosperm tissue are removed from such seeds, baring the 
embryos, many of the cotyledons enlarge slowly and, if in the light, 
become green. After a week or two some of the radicles show geotropic 
bending and slow elongation, but normal growth does not occur. 
When one or both of the seed coats are removed from after-ripened 
seeds germination is accelerated even under conditions under which the 
seeds would germinate in a few days if the coats were left intact. An 
example of this is furnished by Newtown Pippin seeds which were put 
22329—23 - 3 
