TWIN HYBRIDS OF OENOTHERA HOOKERI T. AND G. 283 



and the reciprocal combination, Oe. syrticolaxOe. suaveolens, and Oe. 

 biennis ChicagoxOe. suaveolens (Opera VII, p. 242). Moreover the 

 hybrids of Oe. Lamar ckianaxOe. suaveolens are uniform, whereas the 

 reciprocal cross gives the usual twins. In all these respects Oe. 

 suaveolens is analogous to Oe. biennis and the question arose whether 

 it would also be so in its behavior towards Oe. Hookeri. I studied 

 both the reciprocal combinations but cultivated for Oe. Hooker ix 

 Oe. suaveolens ony one generation, which I found strictly uniform. 

 I made this cross twice, in 1913 and 1915, and had in 1914 a progeny 

 of 90 and in 1916 one of 80 individuals. All of the latter and 25 

 of the former have flowered. They were in many respects like Oe. 

 Hookeri, with reddish, narrow, hairy leaves of an intermediate shape 

 and with the large bright flowers of this species, but still more 

 narrowly resembled the hybrids of the reciprocal cross. 



The results of this reciprocal cross, Oe. suaveolens xOe. Hookeri, 

 are complicated by the high degree of mutibility of the first-named 

 species, as compared with that of Oe. biennis. Otherwise they have 

 been exactly the same as those described above for Oe. Hookerix 

 Oe. biennis. Therefore I shall use here the same names of rubiennis 

 and Hooker /-like for the hybrids. The first generation was uniformly 

 rubiennis but in the second and third generation the Hookeri-Uke 

 were split off in proportions, which indicate a splitting into nearly 

 equal parts. The figures were 53 percent in the second and 31 percent 

 in the third, the latter figure being an average of the offspring of 

 eight individuals of the second generation, all of which showed the 

 splitting. 



As already said the purity of this pedigree was diminished by the 

 appearance of deviating types, which were evidently due to the 

 mutability of Oe. suaveolens. In the first generation two narrow-leaved 

 specimens appeared, and in the second and third, plants were seen 

 with the pale broad leaves of the mutant lutescens (Opera VII, p. 

 242), but evidently hybrids between this form and Oe. Hookeri. 

 The progeny of both these types of mutants was uniform, as far 

 as investigated. Some other deviations were observed, but not 

 closely studied. 



Oenothera suaveolens is heterogamous in many respects, and so the 

 same explanation, as given above, may be applied to this case. 



I will now describe the details of my experiments. 



I made the cross in 1913 between two annual individuals of my 

 races, and had in 1914 a first generation of 60 specimens, all of which 

 grew to a height of 1 meter. Most of them flowered in August. They 



