298 Reduplication in Gametic Series 



number of plants required. Thus the coupling between erect standard 

 and blue is on the 127 : 1 : 1 : 127 system, and if the repulsion were of 

 similar intensity we should expect only one hooded red in every 65,536 

 plants. We may, however, state that in this particular case we have 

 grown over 4000 plants without meeting with a hooded red, so that 

 the facts, so far as they go, point to a high intensity of repulsion for 

 factors exhibiting a high intensity of coupling. It is obvious that the 

 relation can only be worked out where the intensity of repulsion is low, 

 and it is hoped that the case of the cretin may eventually throw light 

 upon this point when the system in 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 heterozygote 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 the blue colour and long pollen in the sweet pea, we pointed 

 out 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 gametogenesis 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 even 

 more clear in vievr of the fact that we now know a series consisting 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 nine or ten good seeds at the most, so that if we even reckon 

 twelve potential seeds to the pod and eight potential gametic cells to 

 the ovule, the total is still onl}' 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 gametogenesis. Miss Saunders' observations on 

 Mattkiola- and on Petunia'^ proved that in those plants the factors for 

 singleness are not similarly distributed to the male and female cells. 



' From the fact that in maize the endosperm characters are the same as those of the 

 seed itself we know moreover that segregation must have been completed before the 

 divisions at which the male and female cells which constitute the endosperm are set apart. 



- Hep. Evol. Committee E. S. IV, 1908, p. 36. 



2 Jour. Gen. i. 1911. 



