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THE AMERICAN NATURALIST [Vol. XL VI 



wore independently and almost simultaneously rediscovered. 9 

 Mendel's principles have been rephrased by later writers, and 

 they are now usually referred to as the Law of Dominance, the 

 Law of Segregation, and the Law of Recombination, respectively. 



I. The Law of Dominance 10 



This so-called Law is derived from the following principle of 

 Mendel ("Versuehe," etc., pp. 10-11) : 



In der weiteren Besprechung werden jene Merkmale, welche ganz 

 oder fast unveriindert in die Hybride-Verbindnng iibergehen, somit 

 selbst die Hybriden-Merkmale reprasentiren, als dominierende, und 

 jene, welche in der Verbindung Intent werden. als rrccssire bezeicbnet. 



Translated this principle reads: 



Those characters which pass entirely or almost entirely unchanged 

 into the hybrid combination and consequently in themselves represent 

 the characters of the hybrid, are designated as dominant, and those 

 which become latent in the combination are termed recessive. 



Since dominance is rarely absolute this principle is not general 

 and should not be termed a law; indeed Mendel did not claim 

 it as a law. Recent statements of the "Law of Dominance" 

 may be thus summarized: 



When the two parents differ in respect of two contrasted characters, 

 only one, the dominant character, will appear in the hybrid. Domi- 

 nance, however, is seldom perfect, so that the dominant character in a 

 hybrid seldom reaches as full expression as in the dominant parent. 



II. The Law of Segregation. 



Mendel's second principle ("Versuehe," etc., p. 17) is thus 



