218 MASS MUTATIONS AND TWIN HYBRIDS OF 



generation. I shall simply call the plants growing up without rosettes 

 ochracea, and retain for the others the term "biennis" 1 ), but both 

 types had the broad, yellowish leaves of the ochracea of the first 

 generation, and its loose spikes. 1 counted in August 33 per cent 

 of the biennis and 67 per cent of the ochracea type. 



Resuming these descriptions we see that the second generation 

 of the first ochracea hybrids was constant and like the parent in all 

 respects except the rosette character. This was absent in two thirds 

 of the specimens, which thereby were just like their parents, but 

 present in one-third, which returned to the mode of growth of the 

 other grandparent. This disposition may be expressed by the fol- 

 lowing pedigree: 



1914 grandiflora x biennis 



First generation 1915 ochracea biennis 



Second generation 1916 ochracea ochracea biennis biennis 



This pedigree shows the splitting of the biennis character in the 

 first ans second generations and the constancy of the ochracea 

 marks in the second. For the majority of the marks of ochracea 

 it runs parallel to the ordinary scheme for the splitting into laeta 

 and velutina, but for the character of the rosettes it is parallel to 

 that of the laeta and velutina produced by the crosses between 0. 

 Hookeri and 0. Lamarckiana, where the laeta is known to split 

 off velutina in the succeeding generations. The explanation which 

 offers itself is that the annual growth is here dominant over the 

 initial rosettes. These are recessive in part of the first generation, 

 but return in their offspring in one-third of the specimens, in about 

 the same way as in the corresponding formula of Mendel. 1 have 

 not tried to go deeper into these questions, however, which touch 

 the mutability of 0. grandiflora only slightly, but have limited 

 myself to two further experiments. 



0. grandiflora ochracea x biennis. — The results of this cross have 

 been the same as in the pedigree just given, with the exception that 

 the splitting in the first generation fails. The cross was made in 



J ) I would have preferred to call them annual and biennial, since one group 

 assumes the annual habit of O. grandiflora and the other the biennial growth 

 of O. biennis L.; but as I cultivated all of them as annuals, it does not seem 

 advisable to use these terms here. The chosen terms relate obviously to one 

 prominent character; they should not convey the conception that all other 

 characters are the same as in the prototypes of the names. 



