OENOTHERA GIGAS NANELLA, A MENDELIAN MUTANT. 33 



of high stature, and 25 per cent normal high specimens. This may 

 be considered as sufficient proof that the splitting took place after 

 the law of Mendel. 



The dwarfs were counted in June and July, and the degree of 

 development at this time corresponded with the photographs given 

 in my Gruppenweise Artbildung, p. 316, figs. 115 and 116. At this 

 period they are clearly distinct from the normal specimens and so 

 there was no difficulty in counting them. In some specimens of 

 0. gigas mut. nanella the number of chromosomes has been deter- 

 mined and was found to be the same as in 0. gigas itself (28), as 

 was to be expected. Partly on account of this fact, partly in con- 

 sequence of the nearer relationship, the fecundations did not experi- 

 ence the difficulties which are connected with crosses between 

 0. gigas and 0. Lamarckiana mut. nanella. They succeeded fairly 

 well and yielded, as we have seen, relatively large numbers of seeds. 



The Mendelian behavior of the production of dwarfs by means 

 of mutation from 0. gigas, moreover, may be proved in another way. 

 If the mutant hybrids of this form are fertilized by the pollen of 

 0. gigas nanella, the expectation will, of course, be the production 

 of 50 per cent of tall specimens and 50 per cent of dwarfs. But, 

 on account of the smaller viability of the latter, we should have to 

 be content with somewhat smaller numbers. In 1913, therefore, 

 I crossed some specimens of apparently normal 0. gigas with the 

 pollen of a constant race of 0. gigas nanella, my culture being the 

 third generation derived from a mutant of 1910 (Gruppenweise 

 Artbildung, pp. 315-316). I was fortunate in choosing, among 

 some normal plants, two mutant hybrids, and will give the constitu- 

 tion of their progeny, together with that of two normal individuals 

 of 0. gigas, in table V. The numbers of seedlings have been very 

 small in this case, owing to the small degree of fertility of the pollen 

 of 0. gigas nanella. 



Table V. 

 Dwarfs in the first generation of 0. gigas x 0. gigas nanella. 



