362 
GENETICS: B. M. DAVIS 
the hot house was irregular. Complete germination in some species 
required only three weeks, in other forms as much as from six to ten 
weeks, and in some cultures I found a few ungerminated seeds after 
three and one half months. In warm, sunny weather the house during 
part of the day was at 90°F., and these high temperatures were frequently 
followed by a burst of germinations. It is thus clear that the best 
results in experimental germination will be obtained when cultures are 
placed in chambers or incubators the temperature of which can be regu- 
lated with accuracy. 
Hugo De Vries^ has recently published a method of stimulating seed 
germination in Oenothera that seems likely to eliminate largely the 
irregularity and slowness of germination described above. He reports 
that well soaked seeds after being subjected to a pressure of 6-8 atmos- 
pheres for 1-3 days at room temperature will germinate in large per- 
centages when removed to an oven at 30°C. His hypothesis for this 
interesting behavior assumes that the hard inner coats of the Oenothera 
seeds have narrow microscopic slits filled with air and that ordinarily 
water enters the seed with difficulty but under pressure can be forced 
to points where it may readily be absorbed. De Vries thus contributes 
the practical suggestion of an automobile pump and a strong chamber 
such as an autoclave into which receptacles containing the well soaked 
seeds may be packed. If complete germination is not obtained after 
one treatment to compressed air successive treatments alternating with 
normal atmospheric pressure and perhaps variation in temperature 
conditions may bring forward stubborn cultures. 
The residue that is left after germination is believed to be complete 
has in my experience generally ranged from structures fully as large as 
the larger of the viable seeds to structures smaller than seeds, which 
in turn grade into the remains of numerous unfertiKzed, or abortive 
ovules, represented in the seed capsules by a fight brown powder. 
It is an easy matter to determine whether or not the structures 
in the residue, seed-fike in size and appearance, contain an em- 
bryo. The structures may be opened with the point of a needle or 
scalpel, or they may be squeezed flat between the tips of a strong 
pair of forceps. The presence of an embryo is at once made evident 
and the germ may be readily examined. Generally the seed-fike struc- 
tures will be found to be entirely empty or to contain only a trace of 
soft tissue. Structures smaller in size than normal seeds can be exam- 
ined microscopically. The residue may be conveniently preserved as 
a record by arranging the structures on paper and covering them with 
a solution of shellac in alcohol, or with a solution of glue. 
