MUTANTS AND HYBRIDS OF THE OENOTHERAS. 20, 



The calyx-segments are relatively much shorter than the hypan- 

 thium in all individuals of the hybrid showing a dominance of a char- 

 acter of O. biennis, although the actual length of the latter is greater 

 in some individuals than in either parent. The other features of the 

 flowers were variously intermediate. The elongated capsule was pres- 

 ent in all of the individuals of the hybrid, except in the two included 

 in the type of No. 2.27. 



OCCURRENCE OF MUTANTS. 



Among the progeny arising from the cross between 0. lamarckiana 

 and 0. biennis were two individuals which, as early as July 1, were 

 seen to be separable by the variously erect leaves with long petioles 

 in the rosettes. The rosettes were sparse, and the leaves were oblong- 

 lanceolate, obtuse at the apex, broadest about the middle, and more 

 or less abruptly narrowing to the petiole, upon which the narrow 

 wings of the laminae extended nearly to the base. The basal portions 

 of the leaves were deeply and irregularly denticulate. The members 

 of the rosette were minutely pubescent. On July 13 these plants had 

 sent up shoots which soon bore the characteristic leaves, bracts, and 

 flowers of 0. rubrinervis, a mutant which was originally observed by 

 De Vries in 1887. 



The occurrence of mutants in hybrids in which one of the parents 

 appears as a pure strain has long been known and has been described 

 at length by Professor De Vries as occurring at numerous times in 

 his cultures. He found that about 1 per cent of the hybrid progeny 

 of 0. lamarckiana X 0. nanella was composed of mutants, and that 

 about 2 per cent of the hybrid progeny between various older species 

 were mutants in a series of tests made in 1896-1900. (De Vries, 1903, 

 pp. 425, 426.) 



0. rubrinervis was observed by De Vries to arise in the hybrid 

 progeny of 0. lamarckiana X nanella, 0. lata X nanella, 0. lata X 

 lamarckiana, 0. lataX brevistylis, 0. nanella X brevistylis, 0. scintillans 

 X nanella, and 0. lamarckiana X scintillans, to which must be added 

 the experience related above, by which this species was also found in 

 the descendants of 0. lamarckiana X biennis. 



The facts recorded by De Vries indicate that the mutability of the 

 various forms of the evening-primrose is not modified by crossing in 

 any manner. It is a matter of interest in this connection that he has 

 also established the conclusion that the number and amplitude of 

 fluctuating variations exhibited by parental forms are not increased 

 or materially modified in the hybrids. 



