TWIN HYBRIDS OF OENOTHERA HOOKERI T. AND G. 



267 



view is given by corresponding crosses of mut. ocfiracea, since these 

 do not produce a splitting but give a uniform progeny with the 

 characters of laeta. 



In Oe. grandiflora the male and the female gametes have the same 

 hereditary qualities. This is shown by crosses with Oe. mut. ochracea 

 and more directly by the fact that both reciprocal crosses with Oe. 

 Cockerelli give the same twins. The same holds good for the crosses 

 with Oe. Hookeri, as we shall presently see, and this is also an 

 isogamic species. 



I made both reciprocal crosses between my races of Oe. grandi- 

 flora and Oe. Hookeri in 1913 and sowed the seeds for a preliminary 

 orientation in 1914 and for more detailed study in 1915. From these 

 latter I derived the second generations in 1916. Moreover I repeated 

 one of the crosses in 1915, in order to have a first generation for 

 comparison with the second in 1916. These first generations con- 

 sisted always only of two types, which could be sharply distinguished 

 and counted at the time of flowering, in July and August. I found 

 the following proportions: 



Table I 



First generation of Oe. grandiflora xOe. Hookeri. 



The figures come as near to equality as might be expected on the 

 ground of the small size of the cultures. No other types appeared, 

 and therefore one of them must be assumed to spring from the 

 non-mutated gametes of Oe. grandiflora and the other from those 

 which had mutated into ocfiracea. 



The types were the same in the three cultures. The differences 

 were small until the time of flowering. The velutina had long and 

 narrow, more or less hairy leaves like Oe. Hookeri and its stems 

 were dark brown. The laeta had pale brown stems with broader 

 leaves with a wedge-shaped base and almost without hairs. They 

 began to flower about a week befoie the other twin. In August I 

 measured some typical leaves, taking them at the same distance 

 below the spike and found 2.5 x 14 cm. for the velutina, but 3.5 x 15 



