47() 



ON TWIN HYBRIDS. 



crosses of the following table in 1903; had the first generation, which 

 often consisted of only a few specimens on account of the di- 

 minished fertility, in 1905; and counted the forms in the second gene- 

 ration during the flowering-period of 1907. Most of the plants were 

 counted in full flower, some of them, however, in the condition of 

 rosettes of root leaves. Only for 0. muricata x brevistylis the cross 

 was made in 1905 and the second generation grown in 1906. 



Table II 

 Constancy of 0. laeta and 0. velutina in second generation 



Cross 



0. biennis x Lamarckiana 



0. biennis cruciata x Lamarckiana . . 



0. muricata x Lamarckiana 



0. biennis x rubrinervis 



0. biennis cruciata x rubrinervis 



0. muricata x brevistylis 



Total 



122 



131 



I also tried this result by counting seedling plants as soon as they 

 clearly showed their differentiating marks. From 0. laeta seed I got 

 only laeta; from 0. velutina seed only velutina. The observed cases 

 for 0. /a^fa were: 0. biennis x rubrinervis {\50),O. biennis cruciata x 

 Lamarckiana (18), the same x 0. rubrinervis (143); and for 0. velu- 

 tina, 0. muricata x Lamarckiana (126), the same x 0. rubrinervis 

 (195), and the same x 0. brevistylis (190). The figures in paren- 

 theses show the number of seedlings observed; together they give 

 311 seedlings of 0. laeta and 511 of 0. velutina. 



It should be stated here that in the cross between 0. muricata and 

 0. brevistylis the character of the last-named species followed the 

 Mendelian law in the case of both of the twins. The 34 0. laeta 

 contained 30 per cent., and the 57 0. velutina 21 per cent., together 

 also 26 per cent., of short-styled individuals, which bore in their 

 leaves and flower-buds and in the flattened lobes of their stigma all 



