'Das Entdeckte Geheimniss' s. 345.); 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 of each variety was prepotent on its own stigma
over that of all other varieties, but I have no evidence on this point. 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 cannot have been injured by,
castration. Girou de Buzareingues crossed what he designates three varieties
of gourd (16/21. Namely Barbarines, Pastissons, Giraumous: 'Annal. des Sc.
Nat.' tome 30 1833 pages 398 and 405.), 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 (16/22. 'Memoire sur les Cucurbitaceae' 1826 pages 46, 55.), 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. (16/23. 'Annales des Sc. Nat.' 4th series tome 6. M. Naudin considers
these forms as undoubtedly varieties of Cucurbita pepo.) Sageret (16/24. 'Mem.
Cucurb.' page 8.) has observed that certain melons have a greater tendency,
whatever the cause may be, to keep true than others; and M. Naudin, who has
had such immense experience in this group, informs me that he believes that
certain varieties intercross more readily than others of the same species; but
he has not proved the truth of this conclusion; the frequent abortion of the
pollen near Paris being one great difficulty. Nevertheless, he has grown close