470 BOTANICAL GAZETTE [DECEMBER 
ture 21.5°, December 2-11, 1909. In this case 96 per cent of the 
lowers, and 33 per cent of the uppers germinated; and the lowers 
averaged 30 mm. in length, the uppers 1omm. The controls were 
injured in some way, but all had germinated. A comparison of 
these figures with those at 90 mm. pressure, temperature 21-22.6° 
(table I), using seeds almost a year old, shows that fresh seeds have 
as high a percentage of germination and a more rapid growth than 
the old seeds under reduced pressure. 
In another experiment, however, seeds collected green in 1910 
were tested along with seeds a year old, and no germination was 
secured at 90 or 100 mm. pressure, at 21°, in either crop of seeds. 
In the controls growth was fine, and the 1910 seeds showed a better 
growth than the 1909, just as reported above for seeds eerie 
under the same conditions. 
It is possible that the after-ripening manifests itself in a cae 
either in the lowered demand of the embryo for oxygen, or in an 
increased permeability of the coats to oxygen, or in both at once, 
the change being too slight to affect the results at normal pressure. 
Some experience with these seeds in laboratory exercises in the 
Hull Botanical Laboratory lends force to this suggestion. With 
freshly ripened seeds having the testas intact, the classes fail to get 
the usual cotyledonary germination in pure oxygen atmosphere, as 
was reported by Crocker for the upper seeds of X. canadense 
after 6 days at 21-23°; but in the winter, several months after 
ripening, these same seeds gave good cotyledonary germination in 
pure oxygen. This experience indicates either a decrease in the 
demand for oxygen by the seed, or an increase in the permeability 
of the seed coats as ripening progresses, and corroborates the 
evidence furnished by the experiments on after-ripening. 
It is clear from these experiments that there is a slow progres- 
sive deterioration of the seeds, manifested in the reduced growth 
of the seeds as they become older, which after a few years probably 
causes entire loss of power to germinate.. This deterioration seems 
to be a little more rapid in the lowers than in the uppers, but the 
physiological difference of the two seeds was very evident in the 
oldest seeds, and no doubt remains so long as they will germinate 
at all. 
