in Hybridisation 81 



a perfect colour-series must result. If, for instance, 



A = A 1 +A S , then the hybrids A } a and A 2 a form the 

 developmental series- 



The members of this series can enter into nine different 

 combinations, and each of these denotes another colour*- 



1 A^A 2 2 A,aA 3 I A 2 a 



2 A^A 2 a 4 AjaAji 2 A s aa 



1 A r a 2 A^aa 1 aa. 



The figures prescribed for the separate combinations 

 also indicate how many plants with the corresponding 

 colouring belong to the series. Since the total is sixteen, 

 the whole of the colours are on the average distributed 

 over each sixteen plants, but, as the series itself indicates, 

 in unequal proportions. 



Should the colour development really happen in this 

 way, we could offer an explanation of the case above 

 described, viz. that the white flowers and seed-coat colour 

 only appeared once among thirty-one plants of the first 

 generation. This colouring appears only once in the series, 

 and could therefore also only be developed once in the 

 average in each sixteen, and with three colour characters 

 only once even in sixty-four plants. 



It must, however, not be forgotten that the explanation 

 here attempted is based on a mere hypothesis, only supported 

 by the very imperfect result of the experiment just de- 

 scribed. It would, however, be well worth while to follow 

 up the development of colour in hybrids by similar experi- 



* [It seems very doubtful if the zygotes are correctly represented by 

 the terms A-^aA^a, A 2 aa, A-fla; for in the hybrids J : a, &c. the allelo- 

 morphs A l and a, &c. should by hypothesis be separated in the gametes.] 



B. 6 



