TWIN HYBRIDS OF OENOTHERA HOOKERI T. AM) G. 



269 



Table 2 



Oe. grandiflora xOe. Hookeri. 

 Offspring of the laeta of the first generation. 



Crosses 



Total 



velutina 



Percent 

 velutina 



Mean 



No. 1 .... j 66 



Oe. grandiflora x Hookeri No. 2 I 65 



No. 3 .... || 66 



No. 4 ... . 65 



No. 1 .... jj 57 



Oe. Hookeri x grandiflora No. 2 .... 66 



No. 3 .... i; 61 



No. 4 .... 66 



50 

 28 

 43 

 34 



26 

 53 

 52 

 35 



39 



42 



The seeds of these laeta do not contain any empty grains. I deter- 

 mined the number of germs in one hundred seeds for each of the 

 hybrids of 1915 in the same lots of seeds from which the cultures 

 of 1916 were derived and found for Oe. (grandiflora x Hookeri) 

 laeta 94, 97, 98 and 100 percent of germs, and for Oe. (Hookeri x 

 grandiflora) laeta 92, 93, 95 and 97 percent. 



The total average of our table is 40 percent. This figure coincides 

 almost exactly with that found for the first generation after the 

 cross (41 percent, see above) and therefore would seem to point 

 to the same cause. But into the cross between the two species Oe. 

 grandiflora brings two kinds of gametes, whereas Oe. Hookeri has 

 on'y one, and this condition was assumed to explain the equality 

 of the two groups of hybrids, which the figures seem to indicate. 

 The question arose, therefore, whether the laeta might have either 

 in their pollen or in their egg cells only one kind of the hereditary 

 qualities involved. This question may be answered by fertilizing 

 the laeta with the velutina. This should then produce in one direc- 

 tion a splitting, but in the reciprocal cross a uniform progeny. 



I made these crosses in 1915 and, in order to vary them as much 

 as possible, took the twins from both the reciprocal crosses. I culti- 

 vated the offspring in 1916, counted them at the time of flowering 

 and found the following constitution for the groups: 



Tabel 3 



Oe. grandifloraxOe. Hookeri. 

 Crosses of laeta with velutina. 



Crosses of 1915 



Total 



velutina 



Percent 

 velutina 



Mean 



Oe. (gr. x H.) laeta x (gr. x H.) velutina 

 Oe. (H. x gr.) laeta x (H. x gr.) velutina 



Oe. (gr. x H.) velutina x (gr. x H.) laeta 

 Oe. (H. x gr.) velutina x (H. x gr.) laeta 



69 

 68 



65 



70 



26 

 34 



31 

 34 



38 

 50 



44 



48 

 48 



48 



