OENOTHERA GRANDIFLORA AIT. 209 



It favors in this mutant, as in the species, the rotting of the stems. 



In September I made the following measurements: height 2 m.; 

 leaves of the upper part of the stem 5 x 15 cm. as compared with 

 3.5 x 12 cm., in 0. grandiflora; petals 4.5 mm. as compared with 

 4.0 x 4.2 cm.; tube of calyx 4 x 50 mm. as compared with 2.5 x 

 35 mm.; flower buds 1.2 x 4 cm. as compared with 0.8 x 3.5 cm.; 

 apex of petals with two deep incisions, which, in 0. grandiflora, are 

 often hardly perceptible; lobes of stigma and filaments of stamens 

 much thicker than in the species. All these characters were very 

 striking on the bed and made the culture one of the most showy of 

 my garden, but the ramification was spare in the mutant; in the 

 species it is ordinarily very rich. 



The seeds of mut. gigas are about double the size of those of the 

 species. I determined the amount of germs per hundred seeds for 

 three self-fertilized specimens of my culture of 1916, and found 

 75—88 and 89 with an average of 84 per cent. This is only a little 

 higher than the average for 0. grandiflora itself, 75 per cent (4). 

 In the roots of one of the three specimens mentioned the chromo- 

 somes had been counted by my assistant Mr. C. van Overeem; 

 their number was 28, as in other instances. 



It should be mentioned that the lorea and ochracea mutants from 

 gigas had stout flower buds and large flowers like their sisters, and 

 therefore must be considered as 0. grandiflora gigas lorea and 0. 

 grandiflora gigas ochracea. 



0. grandiflora mut. semigigas. — This mutant of 1915 differs 

 the same way from the species as did the gigas. I did not find any 

 striking difference between the two before the fruits ripened. They 

 were stout in gigas, but small and thin in the other mutant, which 

 for this reason could not be considered as true gigas, but evidently 

 constituted only a semigigas. No fertile seeds could be obtained. 



Since the occurrence of a mutant gigas gives full right to the 

 expectation of mutants of the type semigigas with 21 chromosomes, 

 I find no difficulty in the determination of the described specimen, 

 but its value is only of a confirmatory nature. 



B. Twin hybrids of 0. grandiflora 



One of the most interesting peculiarities of 0. grandiflora is the 

 production of twin hybrids in certain crosses, analogous to the twins 

 of 0. Lamarckiana. This splitting was discovered by Davis (3) and 

 since confirmed by my own experiments (4). The analogy is very 



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