ter to enumerate some of the
human unit characters whose heredity has been traced and which have
been found to Mendelize, but we may mention here a few Mendelizing
units in other organisms in order to give some idea of the kind of
character which behaves as a unit and of the range of the forms which
have been found to show Mendelian phenomena in their heredity. Among
the higher animals one might mention the absence of horns in cattle
and sheep; the "waltzing" habit of mice and the pacing gait of the
horse; length of hair and smoothness of coat in the rabbit and guinea
pig; presence of an extra toe in the cat, guinea pig, rabbit, fowl;
length of tail in the cat; and in the common fowl such characters as
the shape and size of the comb, presence of a crest or a "muff," a
high nostril, rumplessness, feathering of the legs, "frizzling" of the
feathers, certain characters of the voice, and a tendency to brood.
Among plants may be mentioned such characters as dwarfness in garden
peas, sweet peas, and some kinds of beans; smoothness or prickliness
of stem in the jimson weed and crowfoot; leaf characters in a great
variety of plants; in the cotton plant a half dozen characters have
been found to Mendelize; seed characters such as form and amount of
starch, sugar, or gluten; flat or hooded standard in the sweet pea;
annual or biennial habit in the henbane; susceptibility to a rust
disease in wheat. We should not fail to mention that scores of color
characters are known to Mendelize, such as hair or coat color and eye
color in animals and the colors of flowers, stems, seeds, seed-coats,
etc., in plants. The list of Mendelizing traits in different organisms
now extends into the hundreds and is increasing almost weekly.

Before leaving the subject of Mendelism we should say that the
phenomena, as described above in the Andalusian fowl and guinea pig,
are among the simplest known. And while such simple formulas serve to
describe the phenomena of heredity in a large number of instances, yet
in a great many other cases the descriptive formulas are more
complicated. We cannot in this place describe any of these
complications. For a full discussion of these and of the whole subject
of Mendelism the interested reader is referred to Professor Bateson's
work on "Mendel's Principles of Heredity" (1909). It must suffice to
say here that in color heredity, for example, such ratios as 9:3:4 or
12:3:1 in the second filial generation instead of t