130 GENETICS 



indicated above, but they have the disadvantage of 

 being so small that the detection of their distinctive 

 phenotypic characters is attended with considerable 

 technical difficulty. 



What the modern experimenter in genetics desires is 

 an organism, first, that possesses conspicuous distinc- 

 tive somatic characters, and, second, which w411 come to 

 sexual maturity early and breed either in captivity 

 or under cultivation both numerously and frequently. 



The preceding table, compiled chiefly from Bateson ^ 

 and Baur,- might easily be much extended. It shows 

 from what diverse sources confirmatory evidence of the 

 truth of Mendel's law has been derived within the 

 past few years. 



6. The Principle of Segregation 



The essential thing which Mendel demonstrated 

 was the fact that, in certain cases at least, the deter- 

 miners for heredity derived from diverse parental 

 sources may unite in a common stream of germplasm 

 from which, in subsequent generations, they may 

 segregate out apparently unmodified by having been 

 intimately associated with each other. This "law of 

 segregation" depends upon the conception that the 

 individual is made up of a bundle of unit characters. 

 It may be illustrated by the separate flowers picked ^ 

 from a garden which, after being made into a nose- 

 gay, may be taken apart and rearranged without in 



1 "Mendel's Principles of Heredity," 1909. 



'^ " Einf iihrung in die experimentelle Vererbungslehre," 1911. 



