No. 553] MENDELIAN HEREDITY 9 



intentions, one may be led into a paradoxical position in 

 regard to the use of factors. Even admiting that the rep- 

 resentation is purely symbolic, the letters used may unin- 

 tentionally come to stand for different things. Thus in 

 the case first cited, the letter P in the formula vP stood 

 for a residuum that gave pink, but in the formula Vp, the 

 letter p stood for the loss of a P-f actor, yet p is the allelo- 

 morph of P, which latter, as stated, meant the residuum 

 when V was lost. In other words, a double meaning was 

 attached to P, for it stood both for the P-f actor, which was 

 only a part of the residuum, and also for the residuum as 

 a whole. It is this doubleness of meaning that gives the 

 opponents of Mendelian inheritance an occasion to im- 

 pose upon the factorial hypothesis a meaning that is 

 really foreign to it. Admitting that the Mendelians them- 

 selves have not always taken the pains to state explicitly 

 that the symbols represent both a factor and a residuum, 

 there is still little or no justification in imputing to the 

 presence and absence theory the view that a given char- 

 acter, pink color, for instance, is the product of a pink 

 factor alone. The attempt to impute to the factorial 

 hypothesis the same interpretation that Weismann made 

 use of in his theory of determinants rests largely upon an 

 erroneous understanding of the symbolism employed. 

 Weismann identifies each character of the organism as 

 the product of a special determinant. The factorial 

 hypothesis assumes only that the cell in one case is differ- 

 ent from the cell in the other, the difference relating, it is 

 true, to some part, but the character produced may be the 

 result of the whole or of much of the cell, and not of one 

 part alone. 



There is a further difference between these two points 

 of view. A change in a factor may have far-reaching 

 consequences. Every part of the organization capable of 

 reacting to the new change is affected. Though we seize 

 upon the most conspicuous difference between the old 

 type and its mutant, and make use of this alone, every 

 student of heredity is familiar with cases where more 



