No. 636] 



I TIOX 



19 



cliaetial) leaves surrounding the female organ, and, as 

 related in his recent paper (Genetics of Sex in Funaria 

 hygrometer), from them monoecious plants resulted. The 

 proof is thus complete that in a haploid tissue a segre- 

 gation of sex can occur. 



The inference may be drawn that the factors for other 

 characters may similarly be liable to segregate in the 

 haploid state. In this connection I may mention a case 

 which, though as yet obscure, perhaps fulfils this expecta- 

 tion. In botanic gardens a variegated maidenhair fern 

 {Adiantum capillus-V eneris) is grown which has wedges 

 of white tissue irregularly distributed in the segments. 

 This plant produces spores freely,'^ and these give rise 

 to prothallia which in several cultures raised here have 

 always been entirely green. But when ferns arise from 

 these green prothallia by the sexual iii-occss tlioy are of 

 three kinds, green, white, and x aricualcd like the parent 

 plants. The fact that the protluillia should ho all green 

 is entirely unexpected and creates a di-tlnct i^roblem, 

 but it is e^ddent that segregation must occur cither in 

 some of the cell-divisions by which the prothallia pro- 

 liferate, or in those by which the gametes are t'onned; in 

 either case in haploid tissue. This segregation is essen- 

 tially different from that by which the differentiation of 

 organs, such as the archegonia and antheridia, is accom- 

 plished, inasmuch as it relates to elements determining 

 the characters of the next generation. 



From the evidence given it is clear that in a wide view 

 of living things segregation can not be exclusively a 

 property of the reduct ioii-di\ision. and for the ])rcsciit 

 it should be regarde<l a> a |>o>>i]Mlity which may occur 

 at any division in the life cycle. 



