ntogeny and are not inherited; they
represent nutrition varieties, are experimentally demonstrable, and
constitute the subject matter of experimental physiology. (2) The others
are inherited and again transmitted; they belong to the physiology of
the idioplasm. This subject is mainly occupied with the origin of the
determinants, hence with the formation of varieties and species. It is
not the subject of experiment, and constitutes the phylogeny or the
physiology of the formation of determinants. A sub-division of this
subject is occupied with the development of the determinants already
present, hence with the formation of races. It is elucidated especially
by experiments in crossing and may be designated as the physiology of
the development of the determinants.

The morphological phenomena which find their application in taxonomy,
belong exclusively to phylogeny. Their ontogenetic history does not
explain their true significance; this can be known only in a
phylogenetic way by comparison of one phenomenon with those phenomena
from which it has arisen in the course of evolution.

23. PLANT CLASSIFICATION FROM THE STANDPOINT OF PHYLOGENY.

Spontaneous generation has taken place at all times and in all places,
in as far as the necessary conditions were concurrently present. (See
page 47). After spontaneous generation the automatic phylogenetic
evolution begins and advances constantly. Consequently the phylogenetic
line rises from time to time to higher stages of organization and
division of labor, but dies of old age if the automatic perfecting
process ceases. The phylogenetic lines of organisms now living have
therefore an unequal age; those of the most highly developed plants and
animals had their origin in the earliest periods of organic life, those
of the lowest organisms in the most recent periods. Hence no general
genetic relation exists among lines now living; only those that are
nearly related and have reached approximately equal stages of
organization may be regarded as branches of the same phylogenetic stock.
A phylogenetic plant system does not exist in fact, but only in figure.

If genetic relation between two races is assumed, either as a reality or
as a symbol, the degree of relationship is determined in a theoretically
exact manner by the number and length of the phylogenetic steps which
are found either between them both or between them and the common
starting point, according as races belong to the sa