of Heredity 27 



But there are additional and even more significant de- 

 ductions from the facts. We have seen that the gametes are 

 differentiated in respect of pure characters. Of these pure 

 characters there may conceivably be any number associated 

 together in one organism. In the pea Mendel detected at 

 least seven not all seen by him combined in the same 

 plant, but there is every likelihood that they are all capable 

 of being thus combined. 



Each such character, which is capable of being dissociated 

 or replaced by its contrary, must henceforth be conceived 

 of as a distinct unit- character ; and as we know that the 

 several unit-characters are of such a nature that any one 

 of them is capable of independently displacing or being dis- 

 placed by one or more alternative characters taken singly, 

 we may recognize this fact by naming such unit-characters 

 allelomorphs. So far, we know very little of any allelomorphs 

 existing otherwise than as pairs of contraries, but this is 

 probably merely due to experimental limitations and the 

 rudimentary state of our knowledge. 



In one case (combs of fowls) we know three characters, 

 pea comb, rose comb and single comb ; of which pea and 

 single, or rose and single, behave towards each other as a 

 pair of allelomorphs, but of the behaviour of pea and rose 

 towards each other we know as yet nothing. 



We have no reason as yet for affirming that any 

 phenomenon properly described as displacement of one 

 allelomorph by another occurs, though the metaphor may 

 be a useful one. In all cases where dominance has been 

 perceived, we can affirm that the members of the allelo- 

 morphic pair stand to each other in a relation the nature 



It is not the ancestral type that has come back, but something else 

 has come in its guise, as the offspring presently prove. For the first 

 time we thus begin to get a rationale of " reversion." 



