454 BOTANICAL GAZETTE [DECEMBER 
Pisum sativum, Brassica Napus, Lupinus albus, and Cucurbita, 
failed to grow in total absence of oxygen, either in water or in sugar 
solution, at any temperature. It is evident that the organs of 
higher plants vary according’ to species in their need of oxygen 
for growth and germination. 
The results obtained with Xanthium seeds emphasize this vari- 
ability, as will be shown later. A preliminary report of this work 
(26) was published some time ago, since which time the work 
there outlined has beenlargely completed. The problem was sug- 
gested by Dr. WitLtAM Crocker, and has been pursued under his 
direction at the Hull Botanical Laboratory. It is a pleasure to 
acknowledge my indebtedness to him for many helpful suggestions 
during the course of the experiments, and for making during my 
absence from the University of Chicago some accurate determina- 
tions of the vapor pressure present in the os saienties under experi- 
mental conditions. 
Historical 
The literature on delayed germination has been reviewed so 
recently by others that a detailed account of the earlier work is not 
necessary here. Some of the earliest experiments were carried on by 
NosseE (21) during the decade 1870-1880, in connection with the 
testing of agricultural seeds. A little later NoppE and HANLEIN 
(22) tested many weed seeds, obtaining remarkable results; and 
finally HANLEIN (11) reported on a large number of seeds which he 
kept in germinative conditions for 1173 days, many of which showed 
a fraction of 1 per cent of germination, while of Phyteuma spicatum 
L. and Primula elatior Jacq. not a single seed germinated in that 
time. These investigators recognized that the testa in some cases 
excluded water and prevented germination. But when the testa 
allowed water to enter, which was not infrequent, and still no 
germination occurred, both writers refer to this phenomenon as an 
inexplicable “ Ratsel.”’ 
HANLEIN recognized another category of behavior, however, in 
which the resistance of the seed to germinative conditions is not 
external and mechanical, but is internal and protoplasmic. The 
character of the ovule, the origin, character, and age of the fertiliz- 
