226 



MASS MUTATIONS AND TWIN HYBRIDS OF 



adjoining cultures of the first and second generations of the other 

 crosses. It was quite evident that no brunnea and no contraria were 

 present. Especially the brunnea constitute a type so widely different 

 from the others that no error could be possible. 



0. grandiflora ochracea x 0. Lamar cki ana nanella. — Cross of 1914; 

 first generation in 1915, embracing, as in other instances, two sets, 

 one in a box kept until the end of July and the other on the bed; 

 observed during the whole period of flowering. There were 25 and 

 27 ovata and 5 and 3 lutea, but no brunnea nor contraria. 



A resume of these facts, confining the observations to those made 

 in August at the time of flowering, is shown in table VI. 



The conclusion is evident that the gametes of 0. grandiflora 

 ochracea produce, in their crosses with 0. Lamarckiana, only two 

 types, ovata and lutea. These are exactly the same, in all respects, 

 as the corresponding hybrids between the parent species. No brunnea 

 and no contraria were observed. The size of the cultures fully war- 

 rants these conclusions, but is not large enough to give reliable 

 percentage figures. From these facts it is evident that among the 

 triple hybrids of 0. grandiflora x 0. Lamarckiana one type, brunnea, 

 is produced only by the non-mutated gametes of the first named 

 parent, whereas another type, lutea, is produced exactly by the 

 mutated ones. If we assume that one-half of the gametes of grandi- 



Table VI 



flora are unchanged and the other half changed into ochracea, one- 

 half of the hybrids must result from the first group and the other 

 half from the second. This shows that the pure and the ochracea 

 gametes must produce each for one-half ovata and for the other 

 their special hybrid. The figures, calculated in table V, indicate 

 52 per cent ovata, 23 per cent lutea, and 21 per cent brunnea, and 



