445 
Relation to the Germination of Immature Seed . 
germination occurs when the testa is allowed to remain in situ whether the 
seeds are dried previous to sowing or not. When the seeds are not subjected 
to the drying process before sowing, the living testa is responsible for the 
50 per cent, mortality observed. When the seeds are sown after having 
been dried the testa is presumably a dead membrane, and it is now the 
drying of the seed which causes the 50 per cent, mortality observed, just as 
in the case of the bare embryos which had been allowed to dry. 
Experiments conducted by Dr. F. F. Blackman and Miss N. Darwin (4), 
of which an abbreviated account was read at the British Association Meeting 
.held at Sheffield in 1910 , but of which no published record is at present 
available, are significant in relation to the hypothesis put forward above to 
the effect that the living testa of unripe seeds limits the gaseous exchange 
of the embryo in the same way as a continuous film of water. They worked 
with barley grains, the vitality of which had been reduced (by age or by 
immersion in the swollen condition in hot water at 50 ° C. (circa) for twenty 
minutes), but which still showed a full percentage of germination when sown 
under ideal conditions. It was found that slight films of water greatly 
delayed the germination, reduced the germination percentage, and resulted 
in the death of a large proportion of such seeds. The results obtained were 
more or less proportional to the thickness of the water films. 
Conclusions. 
Many authors (see especially Nobbe (19), Maze (18), Windisch (23), 
Eberhart ( 6 ), Atterberg (1), Babcock (2), Kinzel (15), and Kondo (17) ) have 
described experiments dealing with the dormancy or delayed germination 
observed when certain seeds, which, although immature and with a relatively 
high moisture content, have nevertheless attained their full size, are sown 
immediately after removal from the parent plant. The process of drying 
has generally been found to terminate the dormant condition of such seeds. 
Different theories have been put forward to account for the dormancy of 
unripe seeds sown in the moist condition immediately after removal from 
the parent plant (see Kidd and West, 12). In the present paper it has been 
shown that in the case of Brassica alba and Pisum sativum the removal of 
the testa not only accelerated the germination and terminated the dormant 
condition of unripe seeds, but also increased the germination percentage. 
It is clear that the rest period observed when attempts are made to germinate 
unripe seeds fresh from the parent plant may be largely attributed to the 
presence of the testa, and there are strong indications that under these con- 
ditions the living testa limits the gaseous exchange of the embryo. A fact 
which should always be borne in mind in this connexion is that the testa, 
considered as a membrane through which the gaseous exchange of the embryo 
must occur, undergoes great modifications during the ripening and drying 
off of the seed. 
Botany School, 
Cambridge, 1919. 
