TWIN HYBRIDS OF OENOTHERA HOOKERI T. AND G. 277 



Table 8 



Second generation of hybrids of Oe. franciscana. 



The dwarfs of the last cross bore all the characters of the velutina, 

 apart from thejr stature. There were two mutants; viz., one lata in 

 the second, and one with linear leaves in the third instance. We see 

 from this table, that the offspring of the velutina is uniform, but 

 that that of the laeta splits into the same two types as were observed 

 in the first generation and in almost the same numerical proportions. 

 The dwarfs, which were absent in the first generation, reappeared 

 in the second generation from the third cross, but only in that of 

 the velutina and not among the seedlings of the laeta. In all these 

 respects the crosses with Oe. franciscana exactly duplicate those 

 with Oe. Hookeri and therebey give a confirmation of their results. 



Crosses of Oe. Hookeri with Oe. biennis 



The fecundation of Oe. biennis L. with the pollen of Oe. Hookeri 

 gives uniform hybrids, which are constant in their progeny (Gruppen- 

 weise Artbildung 1913, p. 70). The reciprocal cross, however, is one 

 of the few cases among the Oenotheras, in which the first generation 

 is uniform, but the second is dimorphous (idem, p. 140). The first 

 generation has the typical form of Oe. biennis but with the red color 

 of Oe. Hookeri and was called therefore rubiennis. It splits into the 

 same type and another which resembles Oe. Hookeri almost wholly. 

 The rubiennis repeats the splitting in the succeeding generations, 

 but the progeny of the Hookeri-Mke hybrids remains uniform. 



No specimens of rubiennis with a constant progeny have been 

 found. This absence distinguished the pedigree thoroughly from the 

 scheme for a Mendelian monohybrid combination and the difference 

 is enhanced by the fact that the splitting does not affect a single 

 unit, but almost the whole group of the differentiating characters 

 of the two species. The high interest attached to this problem has 



