104 DOMESTICATED ANIMALS AND PLANTS 
Now it is evident that we might have cows with good udders 
and indifferent digestive powers. In other words, milk produc- 
tion is conditioned upon a number of minor factors, each able to 
behave somewhat independent of the others physiologically ; that 
is, to behave as separate unit characters. 
The term ‘unit character’’ is therefore used to indicate such 
fundamentally physiological elements as tend to behave some- 
what independently of each other and to act as units in trans- 
mission from parent to offspring. 
How these units are transmitted from parent to offspring, and 
how they behave in transmission, is the subject of succeeding 
chapters. 
Summary. Each " character” has a real physiological basis, and such 
an ultimate unit of variability is called a “ unit character.” In common par- 
lance we often use the term “character” for what must be the resultant of a 
large number of these units, as when we speak of milk production. 
These unit characters are sometimes difficult to differentiate and identify, 
but often not; as, for example, a single color commonly behaves as a unit, 
while temperament and the more complex functions are evidently the re- 
sultants of many units. 
Exercises. 1. Make a list of the color characters of horses, cattle, sheep, 
pigs, and other domestic animals. 
2. Make a list of the characters common to the horse and the cow; the 
pig and the sheep; the hen and the goose; the hen and the pig.? 
3. Make a list of characters possessed by the one but not by the other of 
the above couplets.” 
1 In this remember that character means any physical part like vertebra or 
rib, hoof or horn, color or odor, as well as any mental trait like timidity or 
fierceness, docility or nervousness. 
2 Thus while the hen and the pig both have round eyes, the hen has feathers 
instead of bristles. What is the seeming hair on the hen? 
