284 TWIN HYBRIDS OF OENOTHERA HOOKERI T. AND G. 



were a uniform lot with the exception of two narrow-leaved plants. 

 They were evidently intei mediate between the parent and very 

 similar to the hybrids of the reciprocal cross. They combined the 

 broader leaves of Oe. suaveolens with part of the reddish tinge of 

 Oe. Hookeri. The two narrow-leaved specimens resembled Oe. Hookeri 

 in this character and in the general color, but had broader and 

 shorter flower buds, hairy leaves and weak stems with some few 

 branches. Their leaves had only half the breadth of those of the 

 typical plants, with the same length. They were probably due to 

 the fecundation of egg cells of Oe. suaveolens, which had mutated 

 into fastigiata or jaculatrix (Opera VII, p. 242) or some other 

 narrow-leaved mutant. 



I cultivated a second and third generation of this narrow-leaved 

 form and found them uniform in all respects, save the flowers. In 

 1915 twenty specimens flowered, among which 10 had the large 

 flowers, common to both parents but the 10 others had very small 

 petals, of 1.5 cm. in length. This size is about the same as for Oe. 

 biennis. I fertilized three large-flowered specimens, and found their 

 progeny uniform in 1916 with 55, 66 and 42 flowering plants. I also 

 fecundated one small-flowered individual but the progeny of this 

 one split in 1916 into 43 small- and 16 large-flowered plants. This 

 points to a Mendelian monohybrid proportion with the small size 

 as a dominant character. I might adduce that among the Hookeri- 

 like hybrids of the splitting branch of the pedigree I fecundated in 

 1915 a large-flowered and a small-flowered specimen and found both 

 constant in their progeny (36 and 53 plants in 1916). If it is allowed 

 to combine all these data we have a complete set of the three types 

 required by the Mendelian formula, viz., constant large and constant 

 small flowers and splitting small-flowered plants, repeating their 

 mark in about three -fourths of their progeny. But I have not further 

 pursued this theme, my aim being only to prove that the size of the 

 flowers varies independently of the others characters, which are 

 always distributed by groups. The same dimorphy in the flowers 

 was seen in 1916 on all the beds from seeds of the typical hybrids, 

 but here the large flowers prevailed. 



In compliance with the terminology used above, I shall here call 

 the typical hybrids of the first generation rubiennis. After self- 

 fertilization they split into rubiennis and Hookeri-like hybrids. My 

 culture embraced 60 plants; they showed the dimorphy in the be- 

 ginning of July, and developed their differences during the flowering 

 period. The rubiennis repeated the marks of the previous year, but 



