Therefore British bees might well be
puzzled how to act in the case of the sweet-pea. I may add that the
staminal tube of another exotic species, Lathyrus grandiflorus, is not
perforated by nectar-passages, and this species has rarely set any pods
in my garden, unless the wing-petals were moved up and down, in the same
manner as bees ought to do; and then pods were generally formed, but
from some cause often dropped off afterwards. One of my sons caught an
elephant sphinx-moth whilst visiting the flowers of the sweet-pea, but
this insect would not depress the wing-petals and keel. On the other
hand, I have seen on one occasion hive-bees, and two or three occasions
the Megachile willughbiella in the act of depressing the keel; and these
bees had the under sides of their bodies thickly covered with pollen,
and could not thus fail to carry pollen from one flower to the stigma of
another. Why then do not the varieties occasionally intercross, though
this would not often happen, as insects so rarely act in an efficient
manner? The fact cannot, as it appears, be explained by the flowers
being self-fertilised at a very early age; for although nectar is
sometimes secreted and pollen adheres to the viscid stigma before the
flowers are fully expanded, yet in five young flowers which were
examined by me the pollen-tubes were not exserted. Whatever the cause
may be, we may conclude, that in England the varieties never or very
rarely intercross.
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