SUMMARY 207 



few unit characters refuse altogether to unite for the 

 production of offspring. From the study of the precise 

 behaviour of those characters in which a pair of 

 parental organisms differ, a flood of light has been 

 thrown upon the phenomena of inheritance. 



We find, as a rule, that opposed to every differen- 

 tiating unit character of one parent there exists a 

 corresponding but different character in the other 

 parent. One parent may have smooth seeds and the 

 other wrinkled seeds, for example. Very frequently 

 the corresponding feature consists in the absence or 

 failure to appear of a particular character, as, for 

 instance, when the non-development of pigment leads 

 to the appearance of white flowers. 



We can now realize how necessary it is, in order to 

 avoid hopeless confusion, to follow the behaviour of 

 each pair of characters in the offspring separately. 



The result of the meeting between the two opposed 

 characters of the same pair we saw to be different in 

 different cases. There may arise in the offspring 

 (i) the appearance of a simple blend of the two parental 

 characters. Or (2) one character may be more or less 

 dominant over the other. Or (3) the combination of 

 the two parental characters in the offspring may give 

 rise to an appearance quite different from that of either 

 of them, very much in the same way as in chemistry 

 oxygen and hydrogen when combined give rise to water. 

 Or (4) we may get further complications in which un- 

 suspected characters, present in an invisible condition 

 in one or both parents, take a part, often giving rise 

 to the appearance of a supposed reversion. 



