Or, as Bailey states it, we are only beginning to find a pathway through
the bewildering maze of hybridization.
This pathway is to be laid out with regard to the following
considerations. We are not to cross species or varieties, or even
accidental plants. We must cross unit-characters, and consider the
plants only as the bearers of these units. We may assume that these
units are represented in the hereditary substance of the cell-nucleus by
definite bodies of too small a size to be seen, but constituting
together the chromosomes. We may call these innermost representatives of
the unit-characters pangenes, in accordance with Darwin's hypothesis of
pangenesis, or give them any other name, or we may even wholly abstain
from such theoretical discussion, and limit ourselves to the conception
of the visible character-units. These units then may be present, or
lacking and in the first case active, or latent.
[307] True elementary species differ from each other in a number of
unit-characters, which do not contrast. They have arisen by progressive
mutation. One species has one kind of unit, another species has another
kind. On combining these, there can be no interchange. Mendelism assumes
such an interchange between units of the same character, but in a
different condition. Activity and latency are such conditions, and
therefore Mendel's law obviously applies to them.
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