THE DETERMINATION OF DOMINANCE. 333 



likewise very doubtful. All that we are entitled to declare or 

 believe on the basis of present actual evidence is that some con- 

 dition in the physico-chemical constitution of these germs cells 

 is present, that makes possible the appearance of one or the 

 other of the two necessary factors which in many instances must 

 be present in later ontogenetic stages, in order to produce a given 

 result. 



Relation of External Conditions to Dominance. 



The question of dominance, while a vital one, has been some- 

 what wrongly attacked. I would hardly wish at the present 

 time to attempt to account for the highly variable results that 

 have been found in the dominance and recessiveness of characters 

 by such explanations as germ contamination, variable potency, 

 alternative dominance, or different types of latency, etc. It may 

 well be true that there is variable dominance, but to what is 

 this dominance due? It seems that many of the experiments 

 in which variable dominance has been found and described were 

 uncritical, and were carried on under the uncontrolled conditions 

 of most breeding operations. In regard to variable dominance 

 or alternative dominance, as a function of the gametic consti- 

 tution of organisms, it is necessary that the operations should 

 be carried on in such a way that surrounding or incident condi- 

 tions are eliminated to the fullest extent ; and experiments must 

 be based, not upon one series, but upon parallel series of similar 

 cultures. As far as ShuU's (1908) attempt to explain this con- 

 dition by various types of latency is concerned, there again the 

 relatively gross conditions under which we are obliged to carry out 

 most of our experiments leaves one open to criticism as to what 

 the results observed were actually due. In other words, the 

 question of dominance, as Bateson (1902) has suspected, is not 

 entirely one of gametic constitution, nor is it one of external 

 conditions, but it is a combination of the two, and this result 

 seems to be fully borne out by the experiments cited in this 

 paper. 



Concerning the nature of the products which result from 

 a given cross, much depends upon how dominance works 

 and what it is that is present in the germ cells. The products 



