170 MENDELISM 



The pollen of the Fj plants (i.e., those plants which 

 were derived from the yellow cross-bred grains) when 

 applied to the female flowers of the same pure white 

 strain of maize, caused in like manner the appearance 

 of white and yellow grains hi equal numbers. This 

 result is equally well expressed by the above diagram 

 on simply regarding the yellow in Fj as the male parent 

 (pollen -parent) instead of as the female parent (seed- 

 parent) of F 2 . 



What is, then, the meaning of these results ? The 

 case is really very simple. The germ-cells (ova and 

 pollen-nuclei) of the cross-bred plants (white x yellow) 

 must be potentially either pure white or pure yellow, 

 with no blending of these characters. Further, the 

 two kinds (yellow and white) of male germ-cells or 

 pollen-nuclei must arise in equal numbers, and the 

 same must be true of the female germ-cells or ova. 

 By this supposition only can the observed facts be 

 explained. If the supposition is true, then, when the 

 cross-bred plant (FJ is crossed again with the pure 

 white form, its white germ-cells give rise to white 

 grains which are of the nature (white x white), and 

 are therefore pure. Its yellow germ-cells give rise to 

 yellow grains which are of the nature (yellow x white). 

 And, since the number of yellow- and white-bearing 

 germ-cells is equal, the number of yellow and of white 

 grains produced in this way is approximately the same. 

 The yellow grains are of the same composition as the 

 original cross-bred grains obtained by crossing pure 

 white with pure yellow, and we have seen that they 

 behave in exactly the same way on further cross- 



