268 TWIN HYBRIDS OF OENOTHERA HOOKERI T. AND G. 



cm. for the laeta. Such a difference is very striking on the bed. 

 The flowers were large and bright, being intermediate in all respects 

 between those of the parents of the cross; they did not differ on 

 the two twins. The dimorphism of the cultures could be seen clearly 

 in the beginning of May, at the time of planting the seedlings in 

 the garden, but at that period some individuals seemed still to be 

 intermediate and to link the two groups together. During the growth 

 of the stems, however, the differences became larger and more 

 evident so as to make the limit between the two groups sharp and 

 fully reliable. The cultures of 1916 have been compared with the 

 offspring of the two types of hybrids of 1915 and wholly confirmed 

 the estimation of the differential marks. 



In 1915 I self-fertMized 8 specimens of laeta and 4 of velutina. 

 The offspring of the latter were uniform in all characters with the 

 exception of the size of the flowers. They embraced 70 individuals 

 in each culture, one-half of which flowered in August. They all 

 resembled their parents. No laeta and no aberrant forms were seen 

 among them. Of the four parents two belonged to the combination 

 Oe. grandiflora x Oe. Hookeri and two to the reciprocal cross. 



The offspring of the self-fertilized laeta offered a motley aspect. 

 Various combinations of the characters occurred, but mostly only 

 in a few individuals. Above these minor differences two types 

 prevailed. One was that of the velutina, uniform among themselves 

 and in all respects like the pure cultures just described. The other 

 was evidently laeta and like the laeta of the first generation, but it 

 was linked to the aberrant forms by so many transitions that it 

 was often difficult to separate them. I had, however, no interest 

 in studying these minor types, and so 1 relied only on the sharp 

 limit between the velutina and the remainder. I counted them in 

 the middle of August, when most of the specimens were in full flower 

 or as near to this phase as was necessary to judge their spikes and 

 flowerbuds. Some few plants had stayed in the condition of rosettes 

 of radical leaves, but even here the differences were shaip enough 

 for the counting. 



I got the following results: 



