s
to avoid error. Dr. Herbert[230] has remarked that variously-coloured
double varieties of the hollyhock (_Althaea rosea_) may be raised with
certainty by seed from plants growing close together. I have been
informed that nurserymen who raise seed for sale do not separate their
plants; accordingly I procured seed of eighteen named varieties; of
these, eleven varieties produced sixty-two plants all perfectly true to
their kind; and seven produced forty-nine plants, half of which were
true and half false. Mr. Masters of Canterbury has given me a more
striking case; he saved seed from a great bed of twenty-four named
varieties planted in closely adjoining rows, and each variety
reproduced itself truly with only sometimes a shade of difference in
tint. Now in the hollyhock the pollen, which is abundant, is matured
and nearly all shed before the stigma of the same flower is ready to
receive it;[231] and as bees covered with pollen incessantly fly from
plant to plant, it would appear that adjoining varieties could not
escape being crossed. As, however, this does not occur, it appeared to
me probable that the pollen {108} of each variety was prepotent on its
own stigma over that of all other varieties. But Mr. C. Turner of
Slough, well known for his success in the cultivation of this plant,
informs me that it is the doubleness of the flowers which prevents the
bees gaining access to the pollen and stigma; and he finds that it is
difficult even to cross them artificially. Whether this explanation
will fully account for varieties in close proximity propagating
themselves so truly by seed, I do not know.

The following cases are worth giving, as they relate to monoecious
forms, which do not require, and consequently have not been injured by,
castration. Girou de Buzareingues crossed what he designates three
varieties of gourd,[232] and asserts that their mutual fertilisation is
less easy in proportion to the difference which they present. I am
aware how imperfectly the forms in this group were until recently
known; but Sageret,[233] who ranked them according to their mutual
fertility, considers the three forms above alluded to as varieties, as
does a far higher authority, namely, M. Naudin.[234] Sageret[235] has
observed that certain melons have a greater tendency, whatever the
cause may be,