on the axis, and of the seeds in the capsule,
sometimes leads, through a freer flow of sap, to changes of structure; but
these changes are often due to reversion. Modifications, in whatever manner
caused, will be to a certain extent regulated by that co-ordinating power
or _nisus formativus_, which is in fact a remnant of one of the forms of
reproduction, displayed by many lowly organised beings in their power of
fissiparous generation and budding. Finally, the effects of the laws, which
directly or indirectly govern variability, may be largely influenced by
man's selection, and will so far be determined by natural selection that
changes advantageous to any race will be favoured and disadvantageous
changes checked.

Domestic races descended from the same species, or from two or more allied
species, are liable to revert to characters derived from their common
progenitor, and, as they have much in common in their constitutions, they
are also liable under changed conditions to vary in the same manner; from
these {356} two causes analogous varieties often arise. When we reflect on
the several foregoing laws, imperfectly as we understand them, and when we
bear in mind how much remains to be discovered, we need not be surprised at
the extremely intricate manner in which our domestic productions have
varied, and still go on varying.

* * * * *

{357}

CHAPTER XXVII.

PROVISIONAL HYPOTHESIS OF PANGENESIS.

PRELIMINARY REMARKS.--FIRST PART:--THE FACTS TO BE CONNECTED UNDER A
SINGLE POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION--THE
DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE
FUNCTIONAL INDEPENDENCE OF THE ELEMENTS OR UNITS OF THE
BODY--VARIABILITY--INHERITANCE--REVERSION.

SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY
ASSUMPTIONS ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE
SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART--CONCLUSION.

In the previous chapters large classes of facts, such as those bearing on
bud-variation, the various forms of inheritance, the causes and laws of
variation, have been discussed; and it is obvious that these subjects, as
well as the several modes of reproduction, stand in some sort of relation
to each other. I have been led, or rather forced, to form a view which to a
certain extent connects these facts by a tangible method. Every one would
wish to explai