1915] DE VRIES—OENOTHERA BIENNIS IgI 
In the empty seeds the embryo develops only a little, just 
enough to stimulate the seed coats to an almost normal develop- 
ment, in size as well as in structure. For the most part these 
empty seeds are a little smaller and especially a little less broad 
than the others, and can,therefore easily be picked out of a sample. 
But quite a good many are externally exactly like good seeds 
and cannot be distinguished from them without being opened. 
RENNER states that about one-half of the seeds are in this empty 
condition. 
By means of a hard steel needle with a curved tip it is easy to 
make the seeds burst, especially after a thorough wetting. The 
seeds which contain a healthy embryo will discharge it; the 
unhealthy seeds will protrude a slightly brownish pulp; and the 
empty seeds show the lack of contents, except a thin layer of 
endosperm in the embryo sack. The various groups may be 
counted out in this way, but the limits between the originally 
empty seeds and those which have become more or less empty by 
an early decaying of their germs are not sharp and often dependent 
upon the health conditions of the seed-bearing individual. 
Among the seeds with a normal and healthy embryo some will 
germinate during the first days after sowing, especially if the 
temperature is a favorable one. Others will follow sooner or later, 
some after weeks or months, while still others may remain dormant 
for years. It is not an uncommon case that the proportion of the 
rapidly germinating seeds is a very small one, and in this case 
a large quantity of seed is necessary to secure a small number of 
seedlings. Moreover, in those cases where the seeds do not pro- 
duce a uniform progeny, but a mixture, as, for example, with twin 
hybrids or in hybrid splitting, the possibility cannot be denied that 
the numerical proportion of the components of the mixture may 
be different for the rapidly germinating seeds as compared with 
the others. In other words, percentage figures may be influenced 
to some degree by the occurrence of a more or less considerable 
Proportion of dormant seeds. 
In order to ascertain the value of this objection, I have made 
from time to time cultures in which the rapidly germinated seed- 
lings were planted out separately from the slower ones. As a 
