410 BOTANICAL GAZETTE [MAY 
which disappear with subsequent weeks. Hence the after-ripening 
of the seed occurs independent of the shell coats. 
2. The after-ripening occurs along with the drying of the seed, 
but independent of the water content, as air-dried seed soon after 
harvest yields lower germinative percentages than seeds of similar 
moisture content the succeeding spring. 
3. The germination seems unaffected by light. : 
4. Exclusion of water by the true seed coat does not seem to 
explain after-ripening. 
5. The delay in germination is occasioned by restriction in the 
supply of oxygen, which thus acts as a limiting factor to germina- 
ion. The seed coat is probably an obstruction to oxygen entry. 
This general situation seems pointed to by the combined results 
obtained by breaking and searing the seed coat; by removal of the 
embryo; by germinative percentages obtained in varying concen- 
trations of oxygen, both below and above the normal of the air; 
by direct measurement of the rate of oxygen intake with intact and 
seared seeds, and with seeds in varying concentrations of oxygen. 
6. The exact nature of the changes in the seed which constitute 
after-ripening cannot be stated positively. However, the data 
obtained seem to point to an increased permeability of the seed 
coat to oxygen, together with a rise in the embryo acid content, 
which is accompanined by increased water-absorbing power of the 
embryo. 
I wish to acknowledge the cooperation of Dr. WILLIAM 
CrocKER who suggested the above problem, and has throughout 
been ready with helpful suggestions. I am also indebted to Miss 
Eckerson for bibliographical material, and to my father, Mr- 
J. R. Arwoon, for assistance in the tedious labor of preparing the 
seed for tests. 
LITERATURE CITED 
1, ABDERHALDEN, E., und Dammuann, Uber den Gehalt ungekeimter und 
gekeimter Samen verschiedener Pflanzenarten an peptolytischen Fer- 
menten. Zeitschr. Physiol. Chem. 57: 332-338. 1908. 
2. APPLEMAN, CHARLES O., Physiological behavior of enzymes and carbohy- 
drate transformations in after-ripening of the potato tuber. 
§2:306-315. 1911. 
