4o6 BOTANICAL GAZETTE ti>ECEMBER 



only laeta; from O. velutina seed only velutina. The observed cases 

 for O. /a^/a were : O. biennis Xrubrinerv is (150), O- biennis cruciataX 

 Lamarckiana (18), the sameXO. rubrinervis (143); and for O- 2;e/w- 

 tina^ O. muricataX Lamarckiana (126), the sameXO. rubrinervis 

 (195), and the sameXO. brevistylis (190). The figures in parentheses 

 show the numbers of seedhngs observed; together they give 311 

 seedlings of O. laeta and 511 of O. velutina. 



It should be stated here that in the cross between O- muricata and 

 O. brevistylis the character of the last-named species followed the 

 MendeUan law in the case of both of the twins. The 34 O. laeta 

 contained 30 per cent., and the 57 O. velutina 21 per cent., together 

 also 26 per cent., of short-styled individuals, which bore in their 

 leaves and flower-buds and in the flattened lobes of their stigma all j 



the characteristics of their male grandparent. The O. brevistylis 

 character is thereby shown to be independent of the hereditary units 

 which cause the production of the twins. 



The third and fourth generations have been cultivated in only one 

 case, as yet, which was a cross made between O- muricata and the 

 pollen of O. Lamarckiana in 1901. The O. laeta in this case was 

 entirely sterile, and so only the O. velutina could be studied. It 

 gave a constant progeny of small extent, the fertility in artificial self- 

 pollination remaining in a diminished condition. 



TABLE III 



Constancy of O. velutina dxiring fotjr generations 



Cross oj O. muricataX 0, Lamarckiana 



O. laeta from 

 Generation Q. laeta O, Telutina O. velutina 



Cross, 1 901 



ist generation, 1902 35 (sterile) 35 



2nd generation, 1903-4 — 27 



3rd generation, 1905 — 53 



o 

 o 



1907 — 60 o 



All in all 175 plants were observed, all bearing the same characters- 



The phenomenon of twin hybrids seems to be very rare in plants. 



There can be do doubt that its occurrence in Oenothera Lamarckiana 



is intimately connected with at least part of the special maimer in 



which this species displays its mutability. The production of some 



of the mutants seems to be ouite dpnendpnt imnn \t fhnuah that of 



y 



r 



1 



i 





