1915] DE VRIES—A MENDELIAN MUTANT 341 
mut. semialta and mut. debilis. The latter is, on the average, about 
half as high asthe former. This curious segregation repeated itself 
in the next generation in 1914, not from all the individuals, but 
from only one of the two whose offspring have been tried in this 
respect. 
Similar proofs of latent mutations of sexual cells may evidently. 
be expected to occur in other strains also and will have to be looked 
for in all cases of an unexpectedly high degree of mutability. 
I will now return to my experiments on the production of dwarfs 
by O. gigas. In order to obtain specimens of O. gigas yielding a 
high percentage of dwarfs from their seeds, I sowed in 1911 seeds 
of my pure strain, cultivated the plants as biennials, and fertilized 
_ them in 1912 by their own pollen, in bags. They were vigorous 
plants of the fourth generation (Gruppenweise Artbildung, p.175), 
and yielded a large harvest of seed, which was sown in 1913, and 
served as a criterion, since no essential differences were to be seen 
on the plants themselves. Moreover, I used the seeds of some good 
biennial specimens of the previous or third generation. The 
ancestors of all these plants had been fertilized by myself in bags 
down from the mutant in 1896 which started the race. The harvest 
of 1912 and 1910, sown in 1913, gave the result as shown in table IT. 
TABLE II 
A. PERCENTAGES OF DWARFS AMONG OFFSPRING OF O. gigas 
Generation — Total of seedlings Dwarfs agp oes e of 
4th generation........ I 174 ° 0.0 
Tasos Cauk ees 2 176 I 0.6 
a ee ies 3 IQI 34 17.8 
ar cry ek ok 4 154 I 0.6 
mee roe eG 5 166 I 0.6 
3rd generation........ 6 164 ° 0.0 
ME ee 7 43 I 2.3 
er eee a 8 52 ro) 0.0 
ie we ee 9 132 2 1.5 
Bae UT 10 130 ° 0.0 
From a second strain, derived from the same mutant and 
described in my Gruppenweise Artbildung (p. 175), I had in 1911- 
1912 nine biennial specimens which yielded a sufficient harvest. 
