INCOMPLETENESS OF SEGREGATION 173 



containing the dominant character derived from the impure 

 dominant parent. 



There is not the slightest doubt that some characters 

 do behave in this manner, for Mendelian inheritance is 

 established by an enormous number of experimental results, 

 but it is also a fact that many characters are most definitely 

 not transmitted according to " Mendel's law." Instead of 

 separating out in successive generations of individuals, they 

 blend and remain blended. There are also some characters 

 that are intermediate, that is to say, they only follow 

 Mendel's law to a limited extent and not entirely. 



Taking the Mendelian characters first, we find that the 

 degree of segregation varies a great deal. In some cases, as 

 with the tallness and dwarfness, the colour of the flowers 

 and of the unripe pods in peas, segregation appears almost, 

 if not quite complete. If all Mendelian characters behaved 

 in this way, it would be conceivable that one character 

 migjat be represented by one entity or unit. For instance, 

 the tallness would be represented by one entity, dwarfness 

 by another, and these would be distributed singly to the 

 gametes. Such cases are, however, rare, and there are few 

 experiments which give such simple results. The suggestion 

 is very strong, that besides the two characters which appear 

 in the offspring in an alternative manner, other characters 

 of the same order may also be represented. In animals the 

 first generation often differs from both parents with regard 

 to a particular character, and this character of the hybrids 

 in subsequent generations apparently splits up again into 

 the two parent characters, dominant and recessive. Take 

 for the sake of simplicity one character only, colour. When 

 two different-coloured animals are crossed, the first genera- 

 tion is generally different from either of the parents, although 

 the two original colours may be extracted in a more or 

 less pure form in subsequent generations. Sometimes the 

 mixture of colour characters is still more obvious. For 

 instance, Correns crossed the white and yellow varieties 

 of the Marvel of Peru (Mirabilis jalapa), both of which, 



