A PHYSIOLOGICAL AND CHEMICAL STUDY OF 
AFTER-RIPENING 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 170 
SopHiA ECKERSON 
Many seeds and spores require a long time for germination. 
The term “after-ripening’”’ has come into rather genera] use to 
designate the changes in the seed during this period. It is often 
loosely used to include disintegration of the seed coats as well as 
protoplasmic or metabolic changes in the embryo. It seems better 
to limit its use, as has been done in this laboratory, to those cases 
where the delay is due to characters of the embryo. In the majority 
of seeds thus far investigated, the delayed germination is due to the 
exclusion of water or of oxygen by the seed coats. A few seeds have 
been studied, however, which do not grow when all coats have been 
removed and the embryo put in good germinating conditions. 
Some change within the embryo is necessary before germination, 
that is, lengthening of the hypocotyl, can take place. This process 
is what we mean by “after-ripening.”” 
Nose and HANLEIN (45), WIESNER (52), Jost (29), and others 
assume, in cases where water enters the seed coat, that growth after 
a long period is due to some change going on within the embryo 
during the seemingly dormant period. This has been determined 
definitely for only three or four species. 
Lakon (35) finds that the delayed (1-2 years) germination of 
Pinus silvestris, P. Strobus, and P. Cembra is not due to coat char- 
acters. With the coats broken or removed, the time required for 
germination was not shortened. Seeds of Fraxinus excelsior (36) 
sown in the spring do not germinate until the following spring. _ In 
the mature seed the embryo occupies about half the space within 
the endosperm; the rest is occupied by a mucilaginous substance. 
During the year that the seed lies in the ground, the embryo grows 
in length and fills the seed coat. Since the embryo is fully 
matute at maturity of the seed, but a period of growth is 
Gazette, vol. 55] [286 
