184 A Defence of Menders 



the great irregularities seen in the Telephone group, he 

 writes : 



"Taking these results together with Laxton's statements, 

 and with the evidence afforded by the Telephone group of 

 hybrids, I think we can only conclude that segregation of seed- 

 characters is not of universal occurrence among cross-bred peas, 

 and that when it does occur, it may or may not follow Mendel's 

 law." 



Premising that when pure types are used the exceptions 

 form but a small part of the whole, and that any supposed 

 absence of "segregation" may have been variation, this 

 statement is perfectly sound. He proceeds : 



" The law of segregation, like the law of domi- 

 nance, appears therefore to hold only for races of particular 

 ancestry [my italics]. In special cases, other formulae expressing 

 segregation have been offered, especially by De Vries and by 

 Tschermak for other plants, but these seem as little likely to 

 prove generally valid as Mendel's formula itself. 



"The fundamental mistake which vitiates all work based 

 upon Mendel's method is the neglect of ancestry, and the 

 attempt to regard the whole effect upon offspring, produced by 

 a particular parent, as due to the existence in the parent of 

 particular structural characters ; while the contradictory results 

 obtained by those who have observed the offspring of parents 

 identical in certain characters show clearly enough that not 

 only the parents themselves, but their race, that is their ancestry, 

 must be taken into account before the result of pairing them can 

 be predicted." 



In this passage the Mendelian view is none too precisely 

 represented. I should rather have said that it was from 

 Mendel, first of all men, that we have learnt not to regard 

 the effects produced on offspring "as due to the existence 

 in the parent of particular structural characters." We 

 have come rather to disregard the particular structure of 



