HOW CHARACTERS BEHAVE 151 
be seized upon when found, and it will be discovered, as we 
should expect, that a few of them will breed true, but that most 
of them will break up, like other hybrids, into a variety of forms. 
Apparently quite independent of this, however, new forms 
occasionally arise by methods that do not seem to involve cross- 
ing. For example, polled or hornless cattle occasionally arise 
spontaneously, as we say; that is, without crossing or other 
known cause. Albino strains arise frequently in nearly all races. 
Thus we have white cattle, horses, sheep, dogs, cats, pigs ; and, 
among wild animals, deer, bears, wolves, rabbits, mice, and rats, 
most of which are known to breed pure. 
In a few cases, notably with sheep, the albino strain has 
been the favorite for obvious reasons, and the older stock, the 
brown or so-called black sheep, is well-nigh lost. With pigs 
the preference is about evenly divided between the black and 
the white. 
Among plants mutation is even more common or else more 
noticeable than among animals, and much of it arises from what 
is technically known as bud variation. Thus a peach tree may 
bear peaches in the usual way for a number of years, when 
suddenly one or two limbs or possibly the entire tree may 
bear a crop of nectarines for a year or so, and then resume 
the bearing of peaches. 
The moss rose is a mutant of the common wild rose, which 
is the parent of all cultivated varieties. The strangest thing 
about bud variation is that the mutants thus arising often drecd 
true, as do the moss rose and the nectarine. 
The weeping habit among the willow, birch, beech, and other 
species of trees; the appearance of smooth among thorny or 
hairy strains, like the smooth gooseberry ; and the reverse of 
this, namely, the sudden appearance of hairy or fuzzy strains 
among the smooth, —all these are now known as mutants. 
1 Certain red strains of swine have been built up mostly by selection, though 
possibly to some extent by mutation, the only red foundation being the reddish- 
tan tinge on the end of the hair of the wild boar. 
