54 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 



The recurrence of known mutants of 0. lamarckianawas observed. 

 O. mbrinervis appeared among the hybrid progeny of O. lamarck- 

 iana X 0. biennis, in which imperfect castration had been accomplished 

 and the parental strain appeared in the cultures. It appears therefore 

 that the mutant may be considered as a derivative of the one parent 

 purely, although the possibility is not excluded that it might have come 

 as a hybrid strain, as has been observed by De Vries in several crosses. 

 Better authenticated mutants were seen to arise from seeds obtained 

 from purely fertilized plants of O. lamarckiana grown in the botanical 

 garden at Amsterdam in igoi ; also from seeds of the same species 

 gathered in the New York Botanical Garden in 1903 after similar 

 precautions had been observed. 0. albida , 'scintillans , gigas, oblonga, 

 subovata, and O.elliptica were found among the mutants, offering evi- 

 dence of the indubitable occurrence of the mutants in purely fertilized 

 seeds, and also that O. lamarckiana has not reached the end of its 

 mutative period. Furthermore, seven forms not definitely assignable 

 to any of the known mutants of this parent were found, showing that 

 the range of the mutability of the species had been extended by 

 unknown causes, but which were included in an environment of 

 cultural conditions extremely favorable to rapid and vigorous growth 

 and development. It seems safe to assume, therefore, that mutation 

 is induced, or at least increased, by favorable, not adverse conditions, 

 though the duration of the experiments has not been sufficient to 

 permit an analysis of this phase of the subject. 



0. gigas, the species most recently tested in the mutation -cultures 

 in New York, was seen to agree in stature and habit with the indi- 

 viduals grown in the original locality at Amsterdam. Only about 

 half of the individuals could be brought into bloom during the first 

 season, although it was extended to ten months by special methods of 

 culture — a fact in accord with the behavior of the plant in De Vries 's 

 cultures. The constancy of the species also extends to its variability 

 as to the forms of the leaves, an'attribute also previously recognized. 



The results of the statistical studies show that some of the unit- 

 characters of the mutants have a much greater variability than the 

 corresponding features of the parent-form, and the greater amplitude 

 of the fluctuations is coupled with a decreased correlation. 



Thus the coefficient of variability of the height of the shoot of 

 7ianella is 31.84 ± 3.16 percent, while that of lamarckiana is 5.37 db 

 0.44 per cent. The coefficient of variability for the number of branches 

 of mbrinervis is 15.0 zfc 1.7 per cent, and for the total length of the 

 branches is 43.7 =k 5.1 per cent, and for the ratio between width and 

 length of the leaves is 10.30 ± 0.20 per cent ; for the number of 



