No. 636] GK\i:il( si:(.l;i:(,Mlo\ 13 



stances to which the conception of ({(uiiiuniicc mii l»c ap- 

 plied, it is the male which commonly carrier tliu i-e- 

 cessive. Segregation of these charact(i> ran Udt in 

 plants so organized be supposed to take place hUer than 

 the constitution of the male and female organs, and 

 therefore the reduction division can not be the one crit- 

 ical moment. The suggestion has been made tliat geiTQ- 

 cells of the missing kinds may be in reality formed and 

 perish before reaching a functional stage. As regards 

 the (Enotheras, where shriveled pollen grains abound, 

 this conjecture is very plausible and probably correct; 

 but wdien, as in the other cases here quoted, the pollen 

 grains are uniformly sound, the hypothesis is inap- 

 plicable and without evidential support. Moreover, even 

 if it were true that certain classes of germ-e(^lls ]HM-isli in 

 one or other of the sexes, that would liar<lly aUcvintc 

 the difficulty, for this differential via])ility would ivinain 

 to be accounted for, being itself a phciKniifiioii of >t"o ro- 

 gation. 



Begonia Dafisii^ is anotliei- curious illii>ti-atiiiii in 

 which segregation must occni- even ('aiTicr. Tlii- ]ilant 

 is a wild, true-breeding six-cics. with oi-ditiary niiuie 

 flowers. All the pollen grains, howcxcr. caiT> doubh'- 

 ness, and used on the female tlowcrs of doulilo ,uive off- 

 spring all double (single being the dominant). The 

 pollen of this plant is as uniform and perfect as that of 

 any species I have ever seen. We must therefore con- 

 elude that the segregation by which singleness separates 

 from doubleness is effected not later than tlie formation 

 of the rudiments of the male and female flowers. Cyto- 

 logical investigation may no doubt show that the distinc- 

 tions between the genetic properties of the male and 

 female are associated with vi>ih]c iiiiclcai- diffcr.'iices. 

 but I see no reason for anticipating that ^ndi ditTcn-nees 

 must exist. (Vlls whi.-h differ in their -enetie poten- 

 tialities must of coni-se (liffei- in pliy-i.'al constitution, 

 but there i> no ivaxui to Hippox. that tlii^ difference 

 need be in any \va\- de]>endent on chronioxune structure. 



9 Jour. Gen., VIII, 1919, p. 199. 



