274 BOTANICAL GAZETTE. [OCTOBER 
became relatively dry. As is found by actual measurement, oxygen 
diffuses through the relatively dry seed coats much more rapidly 
than through those saturated with water. This is indicated again 
by the fact that the soaked upper seeds of X. echinatum germinate 
readily at 25-27° when resting on the walls of corked bottles ‘con- 
taining air, while in soil or between saturated filter papers a tempera- 
ture of 33° is necessary for any considerable germination, The 
upper seeds of every species with seed coats intact can be most 
easily germinated by allowing the seeds to lie on the walls of corked 
bottles of such size that a good oxygen supply is given. In this 
condition the relatively dry coats allow the passage of considerably 
more oxygen, hence germination comes about at lower temperatures. 
The second set of experiments on gaseous exchange is for the 
purpose of determining why high temperatures bring about the ger- 
mination of the upper seeds with the seed coats intact. It imme- 
diately suggests itself that this may be due to one or both of two 
things: the amount of oxygen diffusing through the seed coat may 
rise with the rising temperature, or the amount of carbon dioxide 
evolved may become greater in proportion to the amount of oxygen 
consumed as the temperature rises. 
It is seen in the 6-hour 50-minute column, as well as in the 12 
hour column of Table VI, that the seeds with the coats intact at 
19°, whether upper or lower, take up less than half as much oxyge? 
as is taken up by the seeds at 33°. This indicates that the diffusion 
of oxgyen through the seed coats is much slower at 19° than at cog 
This conclusion, however, needs more direct evidence. Especially 
is this apparent when it is remembered that 19° is slightly below 
the minimum germinative temperature, even with the coats removed, 
and that the amount of oxygen consumed, therefore, may not repre- 
sent the full amount that can diffuse through the coats at 19°, PFO 
vided the consumption on the inside is complete. 
The apparatus in jig. 3 was used for determining accurately the 
effect of high temperatures on the rate of diffusion of oxygen through 
the seed coats. S is a storage bottle for potassium pyrogallate; j, # 
flask from which the oxygen is to be absorbed by potassium pyrogallate; 
t, a seed coat fastened on the end of a glass tube; w, a vial of wate? 
from which a thread reaches the seed coat to keep it wet; ¢, 4 capil 
