264 THE FACTORIAL HYPOTHESIS 
product of the activity of the germ cell may be 
different. All sorts of characters might be affected 
by the change, but certain parts might be more con- 
spicuously changed than are others. It is these more 
obvious effects that we seize upon and call unit 
characters. It is the custom of most writers to speak 
of the most affected part as a ‘‘unit character,’’ and 
to disregard minor or less obvious changes in other 
parts. They frequently speak of a unit character as 
the result of a unit factor, forgetting that the unit 
character may be only one effect of the factor. 
Failure to realize the importance of these two 
points, namely, that a single factor may have sev- 
eral effects, and that a single character may depend 
on many factors, has led to much confusion between 
factors and characters, and at times to the abuse of 
the term ‘“‘unit character.” It can not, therefore, 
be too strongly insisted upon that the real unit in 
heredity is the factor, while the character is the prod- 
uct of a number of genetic factors and of environ- 
mental conditions. The character behaves as a unit 
only when the contrasted individuals differ in regard 
to a single genetic factor, and only in this case may 
it be called a unit character. As soon as the indi- 
viduals differ by two or more genetic factors that 
affect the same character the latter can be no longer 
considered a unit. So much misunderstanding has 
arisen among geneticists themselves through the 
careless use of the term “unit character” that 
the term deserves the disrepute into which it is 
falling. 
