in Hybridisation 75 



of the two sorts of pollen may fertilise each separate egg 

 cell. For this reason the separate values must necessarily 

 be subject to fluctuations, and there are even extreme cases 

 possible, as were described earlier in connection with the 

 experiments on the form of the seed and the colour of the 

 albumen. The true ratios of the numbers can only be 

 ascertained by an average deduced from the sum of as 

 many single values as possible ; the greater the number 

 the more are merely chance elements eliminated. 



The developmental series for hybrids in which two 

 kinds of differentiating characters are united contains 

 among sixteen individuals nine different forms, viz., 



Between the differentiating characters of the original stocks 

 A a and Bb four constant combinations are possible, and 

 consequently the hybrids produce the corresponding four 

 forms of egg and pollen cells AB, Ab, aB, ab, and each 

 of these will on the average figure four times in the 

 fertilisation, since sixteen individuals are included in the 

 series. Therefore the participators in the fertilisation are 

 Pollen cells A B + AB + AB + AB + Ab + Ab + Ab + Ab + 



aB + aB + aB + aB + ab + ab + ab + ab. 

 Egg cells AB + AB + AB + AB + Ab + Ab + Ab + Ab + 



aB + aB + aB + aB + ab + ab + ab + ab. 

 In the process of fertilisation each pollen form unites on an 

 average equally often with each egg cell form, so that each 

 of the four pollen cells AB unites once with one of the 

 forms of egg cell AB, Ab, aB, ab. In precisely the same 

 way the rest of the pollen cells of the forms Ab, aB, ab 

 unite with all the other egg cells. We obtain therefore 

 AB AB AB AB Ab Ab Ab Ab 



AB ~Ab aB ~ab AB ^Ab ^B ~ab 

 aB aB aB aB ab ab ab ab 



AB Ab aB ab AB Ab aB ab' 



