There are two possibilities, and both have been
propounded by Darwin. One is the accumulation of the slight deviations
of fluctuating variability, the other consists of successive sports or
leaps taking place in the same direction.
In further lectures a critical comparison of the two views will be
given. Today I have only to show that the mutations of the
evening-primroses, though sudden, comply with the demands made by Darwin
as to the form of variability which is to be accepted as the cause of
evolution and as the origin of species.
Some of my new types are stouter and others weaker than their parents,
as shown by _gigas_ and _albida_. Some have broader leaves and some
narrower, _lata_ and _oblonga_. Some have larger flowers (_gigas_) or
deeper yellow ones (_rubrinervis_), or smaller blossoms (_scintillans_),
or of a paler hue (_albida_). In some the capsules are longer
(_rubrinervis_), or thicker (_gigas_), or more rounded (_lata_), or
small (_oblonga_), and nearly destitute of seeds (_brevistylis_). The
unevenness of the surface of the leaves may increase as in _lata_, or
decrease as in _laevifolia_. The tendency to become annual prevails in
_rubrinervis_, but _gigas_ tends to become [574] biennial. Some are rich
in pollen, while _scintillans_ is poor. Some have large seeds, others
small.
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