330 



case of the cretin may eventually throw light upon this point 

 when the System on which N and F are coupled shall have been 

 determined. 



The question now arises how these gametic Systems are 

 formed. In each the characteristic phenomenon is that the hete- 

 rozygote produces a comparatively large number of gametes 

 representing the parental combinations of factors and comparatively 

 few representing the other combinations. In describing the original 

 case of coupling, namely that between blue colour and long pollen 

 in the sweet pea, we pointed ont that no simple System of 

 dichotomies could bring about these numbers, and also that it 

 was scarcely possible that such a series could be constituted in 

 the process of gameto-genesis of a plant in whatever manner the 

 divisions took place. In saying this regard was of course had 

 especially to the female side, and this deduction has become 

 more clear in view of the fact that we now know a series con- 

 sisting of 256 terms. It is practically certain that the ovules 

 derived from one flower of the sweet pea, even if all collateral 

 cells be included, cannot possibly be arranged in groups of this 

 magnitude. A pod rarely contains more than 9 or 10 good seeds 

 at the most, so that even if we reckon 12 potential seeds to the 

 pod and 8 potential gametic cells to the ovule the total is still 

 only 96, which is much too few. Nevertheless our series of numbers 

 is plainly a consequence of some geometrically ordered series 

 of divisions. 



There is evidence also from other sources that segregation 

 may occur earlier than gameto-genesis. Miss Saunders' observations 

 on Matthiola 1 ) and on Petunia 2 ) proved that in those plants 

 the factors for singleness are not similarly distributed in the male 

 and female cells. The recent work of de Vries on Oenothera 

 biennis and muricata 3 ) has provided other instances of 

 dissimilarity between the factors borne by the male and female 

 organs of the same flower. In all these examples it is almost 

 certain that segregation cannot take place later than the formation 

 of the rudiments of the carpels and of the stamens respectively. 

 The only alternative is that in each sex the missing allelo-morphs 

 are represented by some somatic cells of the sexual apparatus, 



1) Rep. Evol. Comm. Roy. Soc. IV, 1908, p. 36. 



2 ) Journ. genetics, I, 1911. 



3 ) Biol. Centr. Bd. XXXI, 1911, p. 97. 



