No. 579] 



MUTATION EN MASSE 



139 



and furnish an abundance of good seed. It is planned to 

 make a biometrical study of fruit length next year, when 

 the second generation of mut. bilonga will be available. 



In Fig. 8 the two branches on the left are mut. semialta; 

 the two on the right mut. bilonga. The plants which fur- 

 nished the material belonged to an F 4 culture from f. 

 typica, containing five plants of f. typica, 13 of mut. 

 semialta, five of mut. debilis and one of mut. bilonga. 

 In Fig. 9, on the contrary, the contrast is between sister- 

 plants of mut. debilis and mut. bilonga in the progeny of 

 mut. debilis. A comparison of the figures will show the 

 identity of mut. bilonga from the two sources. 



The phenomenon presented by (Enothera Reynoldsii, 

 called mutation en masse for want of a better name, seems 

 of sufficient interest to justify this preliminary paper. 

 The fact that it appears in one of the short-styled, self- 

 pollinating species makes it of especial interest. An ex- 

 planation can hardly be attempted until the interrelation- 

 ships of the various derivations have been worked out by 

 a series of crosses. Nevertheless, it seems clear that 

 mutation en masse bears a certain degree of resemblance 

 to Mendelian segregation. The fundamental mutation 

 which causes the diversity possibly occurs in only one of 

 the two gametes in a generation preceding the one in 

 which diversity becomes manifest. It is masked by the 

 dominance of the parental characters transmitted through 

 the other gamete. Segregation then occurs in the follow- 

 ing generation. No explanation suggests itself for the 

 enormous surplus of dwarfs in the progenies exhibiting 

 diversity, unless perhaps it is that the results are com- 

 plicated by selective germination or selective mortality. 

 At any rate, the ratios thus far obtained do not conform 

 to any Mendelian expectation. Larger cultures, to be 

 grown next year, may prove more enlightening. 



To the mutationist, the most interesting problem pre- 

 sented by (Enothera Reynoldsii is the origin of mut. 

 bilonga from mut. debilis, involving, as now seems prob- 

 able, the origin of a new character. 



