Igr11] SHULL—OXYGEN MINIMUM AND GERMINATION 457 
acters, which exclude or restrict the supply of water, rather than 
to embryonic characters. : 
At about the same time certain German investigators published 
a number of papers dealing with similar problems, which are of 
interest chiefly because of the interpretations of their results. 
CorRENS (3) found a higher percentage of germination in the disk 
seeds of Dimorphotheca pluvialis than in the ray seeds. He ascribed 
the difference in percentage of germination to the different constitu- 
tion of the embryos, but CrocKEeR showed that in the dimorphic 
seeds of Axyris amaranthoides the non-winged seeds were delayed 
by coat characters, and that the percentage of germination did 
not differ when the coats were broken, both showing too per cent 
in three days. 
Ernst (6), working with seeds of Synedrella nodiflora, showed 
that light of various intensities and refrangibility affected the length 
of time necessary for germination, and he attributed not only 
percentage of germination but also the length of time necessary for 
germination to the constitution of the embryo. 
FIscHER’s (8) paper on the influence of hydrogen and hydroxyl | 
ions on seeds of aquatic plants appeared shortly before CROCKER’s 
work on the seeds of the same plants. Fiscuer interpreted his 
results as showing that the ions stimulated and awakened the sup- 
posedly dormant protoplasm to activity, and thus caused germina- 
tion to occur. But as already intimated, it was shown by CROCKER 
that the protoplasm of the seeds of these aquatic plants is not 
dormant, and needs no stimulus except the necessary conditions for 
germination, which are supplied if the testa is removed or broken. 
OsTENFELD (23) found that digestive enzymes of birds favored 
the germination of seeds, but he refrained from ascribing the results 
to the effect of the enzyme on the embryo, saying that the question 
raised by the widely different interpretations of FiscHer and 
CROCKER was an open one. 
Following the work of Ernst mentioned above, KINZEL (12-16) 
has shown that light is a factor in the delayed germination of many 
seeds. The data accumulated show that in some way light of 
various intensities and refrangibility modifies the seed with the 
testa intact. The interpretation in all cases ascribes the results 
