444 Kidd and West.— The Role of the Seed-coat in 
the following way. It was argued that, assuming the hypothesis to be correct, 
these immature seeds, when sown under germinating conditions, must either 
be in a condition in which the limitation of the gaseous exchange of the 
embryo is so great as to become actually harmful (e.-g. in the cases where 
sowing on damp sand is followed by death), or at any rate must be near the 
point at which any further limitation will cause injury. It follows that if we 
impose even for a short period a condition which further limits the gaseous 
exchange of the embryo we should, if our hypothesis is correct, obtain a pro- 
nounced result. In order to further limit the gaseous exchange, the seeds were 
immersed in water for short periods before sowing. The result, as Table VI 
shows, is striking and bears out our hypothesis. Whereas fully ripe dry pea 
seeds will endure immersion in water for several hours without showing any 
obvious decrease in the percentage of germination (Kidd and West, 11 ), the 
unripe pea seeds suffer heavily even after a few hours’ immersion. The 
amount of injury shown is more or less proportional to the period of soaking. 
On the other hand, soaking per se for the periods used in this experiment is 
in no way harmful to the embryo, as is shown by the results of a parallel 
series of experiments with the bare embryos from unripe pea seeds. 
Table VI. 
The seeds used in this experiment were similar to those of category C 
in Table V. Twelve seeds were used in 
each experiment. They were 
sown in garden soil. Temperature i5°-20° 
C. 
Results observed 1 1 days after sowing : 
Condition of 
the Seed. 
Percentage 
Percentage 
Average 
Treatment. 
of seeds 
of vigorous 
length of 
dead. 
plants. 
the shoots. 
/Dried in air for 15 hours before sowing 
20 
58 
2 cm. 
Sown immediately after removal from 
33 
5 ° 
2 » 
Immature. 
With testas 
' parent plant 
Soaked in tap- water for 1 f hours before 
5 ° 
42 
3 
sowing 
Soaked in tap-water for 5 hours before 
58 
33 
2 ” 
i, sowing 
Dried in air for 15 hours before sowing 
0 
50 
2 ’5 
Sown immediately after removal from 
0 
92 
3 ,, 
Immature. 
parent plant 
Soaked in tap-water for if hours before 
0 
100 
4’5 
Without testas 
sowing 
Soaked in tap- water for 5 hours before 
0 
100 
4*5 >1 
sowing 
Mature intact ) 
seeds j 
■ Soaked for 24 hours 
0 
100 
8-5 „ 
The above table also shows results which were obtained with bare 
embryos and with intact seeds which were dried in the air for fifteen hours 
before sowing. The germination of the bare embryos is reduced from 100 
per cent, to 50 per cent, by the drying process, which is thus shown to be 
injurious to unripe pea seeds. A similar reduction in the percentage of 
