igis] • 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 

 0. 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 

 viabihty 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 

 0. 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 spht 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 0. gigas nanella, yield 

 30-43 per cent, theoretically 50 per cent, of dwarfs. 



4. In artificial crosses with 0. gigas the dwarfs follow the law 

 of Mendel. 



5. The production of dwarfs from 0. 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 0. 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 0. gigas and its parent 

 species. 



Amsterdam 



