1906] CROCKER—DELAYVED GERMINATION 277 
rise in temperature when the oxygen supply is diminished by the 
presence of the seed coats. 
This rise in the respiratory ratios with the rise in temperature 
is measured for the entire seed (more than 95 per cent. of which is 
storage material) and not for the actively growing radicle. It is 
probable that for the radicle the respiratory ratio rises far above 
1. This becomes more evident when it is remembered that at 33° 
the radicle grows first, as is normal; but that at 22°, in increased 
oxygen pressures, though it be five atmospheres, the growth of the 
cotyledons first takes place. Here, too, it should be recalled that 
the seed coat is much thicker and more dense over the radicle than 
over the cotyledons, 
From the data of this section two effects of a rise in temperature 
are evident. It increases the rate of diffusion of oxygen through 
the seed coats; and it increases the respiratory ratio somewhat 
with the seed coats removed and markedly with the seed coats intact. 
If CO, be taken as the criterion, it is possible from the data above 
to calculate quantitatively the increase in respiration with a rise in 
temperature from 19° to 33°, when the seed coats are intact. The 
crease in the rate of diffusion of oxygen (if there were no increase 
in the ratio CO,:O,) equals an increase in respiration from 1 to 
1.5 (the average of 1.4-1.6). But the increase in the respiratory 
ratio is from 0.6 at 19° to t.0 at 33°. This then increases the res- 
Piration from 6 units to 10 units. When the two facts that indicate 
an increase in respiration are considered together, it is evident that 
a rise in temperature from 19° to 33° with the coats intact causes a 
tise in the amount of respiration from 0.6 to 1.5; or from 1 unit to 
2.5 units, ‘ 
It is evident from Table V that the seed coats of the lower seeds, 
as well as those of the upper, greatly restrict the amount of oxgyen 
used by the seeds, and that this restriction, though considerable, is 
hot markedly greater in the upper seeds than in the lower ones. 
X. echinatum this rather slight difference in the rate of diffusion 
of oxygen through the seed coats of the upper and lower seeds is 
yet sufficient to give the upper seeds a minimum germinative tem- 
perature of 32° with seed. coats intact, and the lowers 22°; while 
both seeds with the seed coats removed have a minimum germinative 
