60 THE FOUNDATIONS OF SCIENCE 



(R) dwarf, its own germ cells are half D and half 

 R. If self-fertilised, or crossed with a similar plant, 

 on the average of large numbers, it must chance 

 that about half the unions will be between D's and 

 R's to form DR's, while half will be pure bred, being 

 divided equally between DD's and RR's. 



But since " talhiess " is dominant, any plant which 

 contains " talhiess " at all in its composition grows 

 tall, and so all the DR's resemble the DD's outwardly, 

 and we get three-quarters of the seedlings apparently 

 tall. But, when crossed among themselves or self- 

 fertilised, these DR's reveal their true nature in their 

 offspring. 



We may illustrate this scheme in a pedigree 

 diagram 



I I I 



DR DR RR 



In other cases, more complicated relations appear. 

 Qualities may be linked, so that one cannot appear 

 without the other, or may be antagonistic, and never 

 exist together. Other qualities may only be found 

 in one sex, or be dominant in one sex and recessive 

 in another. 



Mendelian characters have been proved to exist in 

 many plants and animals. The insight which this 



