EXPERIMENTAL STUDY OF HEREDITY 65 



be fertilized with either an s-sperm or a w-sperm, giving 

 (s + w) X (s + w) = ss -\- 2sw -{- ww. Since 5 is dominant 

 over w the product should be written: 



55 + s(w) -f- s(w) + ww 



giving in external appearances 35 + iw. Since the re- 

 sult actually observed is what it would be if the gametes 

 were thus "pure" for smoothness and wrinkling, Mendel 

 concluded that they really are, and moreover that each 

 character behaves as a unit, appearing and disappearing 

 in its entirety. 



56. Character-units versus Unit-characters. As just 

 stated, Mendel held that the various visible characters of 

 his plants (dwarfness, for example) behaved as units, 

 either appearing in their fullness, or not appearing at all. 

 From more careful observations we know that such is 

 not the case. A blossom may, for example, be more or 

 less pink, an odor more or less strong, dwarfs are not 

 all the same height, but fluctuate around a mean. We 

 conclude therefore that characters do not behave as 

 units, and that the conception of "unit-characters" is 

 erroneous. The evidence does, however, seem to justify 

 the conclusion that the factor or factors, whatever they 

 may be, 1 that are causally related to the given character 

 do behave as units. We may therefore designate them 

 as character-units. Since they are causally or genetically 

 related to the character they have been called genes (from 

 the root of the Greek word, genesis). They are more 

 commonly known as factors. Quite probably, in many 

 if not all cases, more than one factor is involved in the 

 production of any given character. 



1 Substance or condition, we know not what, within the germ-cells. 



