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THE AMEBIC AN NATURALIST [Vol. XLIX 



in which all the young pollen-grains and embryo-sacs had pre- 

 sumably an equal chance to mature. 



Perhaps a parallel state of affairs exists to-day. De Vries and 

 others have brought to light, in the progeny of (Enotheras, a cer- 

 tain amount of "variation," by no means so striking as can be 

 seen in the progeny of many variety or species crosses, but re- 

 markable chiefly because it could not be explained. In my opin- 

 ion, this "variation" can perhaps be explained by going back, 

 as Mendel did, to the haploid generation. We may, I think, pre- 

 sume that there are certain genetic factors concerned with the 

 development of the young microspore into a complete pollen- 

 grain, and the young niegaspore into a normal embryo-sac. If 

 the plants are heterozygous for one or more of these factors, we 

 get definite ratios of normal and aborted pollen grains, or normal 

 and aborted embryo-sacs. We thus have a population of haploid 

 individuals ('microspores or inegaspores) which show segregation 

 into viable and non-viable. We may expect ratios of normal and 

 aborted haploid individuals of 1 : 1 ; 1 : 3 ; 1 : 7 ; 1 : 15, etc., apply- 

 ing to either pollen-grains or to embryo-sacs, or to both. When 

 we thus have heterozygosity of one or more factors essential for 

 the development of the individuals of the haploid generation, the 



the development of embryo-sacs, 

 (or nearly complete) repulsion. ' 

 will be permanently heterozygou 

 also more or less for any other fac 

 them. (Linkage has been shown 

 where it has been looked for.) \> 



