MENDELISM AND OTHKR METHODS OF DESCENT 229 



ism can express only one set of characters, though it may 

 transmit to posterity an unlimited number of varying equip- 

 ments.' 



Conjugate organisms may give no hint of the presence of a 

 character which the gametes are able, nevertheless, to transmit 

 unimpaired through long series of generations. The behavior 

 of two gametes in the conjugate phase is no criterion of the 

 results of the conjugation, as represented by the new gametes 

 of the next generation. The inheritance of expression-polari- 

 ties is entirely distinct from transmission-inheritance. Expres- 

 sion-polarities may be mutually exclusive, so that polarity of 

 one character implies the abeyance or non-polarity of expression 

 of alternative characters, but there are no indications of such 

 exclusiveness in the transmission of characters. 



If transmission is to be thought of as accomplished by charac- 

 ter-unit particles the indications are that the tendency is to ac- 

 cumulate as great a diversity of particles as possible, instead 

 of excluding any because of incompatibility. Transmission is 

 inclusive, not exclusive. The continued transmission of a 

 character can not be ascertained, of course, unless it be brought 

 into expression, but the possibilities of transmission without ex- 

 pression are now amply demonstrated. To assume that a char- 

 acter has failed of transmission because it remains unexpressed, 

 is entirely gratuitous. 



It remains true, of course, that the characters of the gametes 

 can only become known through their expression in conjugate 

 organisms, but this difficulty of interpretation does not absolve 

 us from the recognition of two distinct factors or problems of 

 inheritance. The problem of potency relates to the polarity or 

 adjustment of unconjugated gametes toward or away from the 

 expression of certain characters. The problem of dominance has 

 reference to the adjustment of gametes in the^conjugate relation. 

 We have yet to learn why the polarity of one gamete overpowers 

 the other and completely controls the development of the con- 

 jugate body, and how the abeyant polarity of the other gamete 

 is able to reassert itself at the period of mitapsis and secure 

 equal representation in the new generation of gametes. 



' Cook,0. F. Transmission Inheritance distinct from Expression Inheritance, 

 Science, N. S., 25 : 911. 1907. 



