1915] DE VRIES—A MENDELIAN MUTANT 345 
fecundation was a difficult one and I got only 38 seedlings, all of 
which developed into tall plants of the stature and character of 
O. gigas (1914). 
In order to study the segregation of dwarfs in the next genera- 
tion I fecundated a number of specimens of the three described 
groups of artificial hybrids and sowed their seed in 1915. On the 
basis of Mendel’s law the expectation is, for all of them, 25 per cent 
dwarfs, or somewhat smaller numbers on account of the lesser 
viability of these dwarfs. The sowings of 1915, counted in May 
and June, gave the results shown in table VI. 
These figures give sufficient proof that the crosses between 
O. gigas and its dwarfs follow the law of MENDEL. 
Summary 
1. Oenothera gigas produces dwarfs (about 1-2 per cent) and 
mutant hybrids of normal stature, which after self-fertilization give 
15-18 per cent, theoretically 25 per cent, of dwarfs. 
2. These mutant hybrids split up, after self-fertilization, 
according to the law of MENDEL, yielding about 18 per cent dwarfs, 
25 per cent normal specimens of tall stature, and 57 per cent hybrids 
of the same type. The latter gave about 21 per cent of dwarfs 
among their progeny. 
3. The mutant hybrids, fertilized by O. gigas manella, yield 
30-43 per cent, theoretically 50 per cent, of dwarfs. 
4. In artificial crosses with O. gigas the dwarfs follow the law 
of MENDEL. 
5. The production of dwarfs from O. gigas by means of mutation, 
therefore, is to be considered as requiring the copulation of two 
gametes, both of which are potentially mutated into dwarfs. The 
mutant hybrids must then be the result of the fertilization of a 
mutated gamete by a normal one. They are correspondingly less 
rare than the dwarfs themselves. 
6. In combination with the fact that the dwarfs of O. Lamarcki- 
ana do not follow the law of MENDEL, either in their origin by muta- 
tion or in artificial crosses with the parent species, these conclusions 
reveal a new differential character between O. gigas and its parent 
species. 
AMSTERDAM 
