I also sowed some of the
same two lots of seeds in poor soil in a shady place in a shrubbery.
Here again the self-fertilised plants from the self-fertilised for a
long time exceeded considerably in height those from the previously
crossed plants; and this may probably be attributed, in the present as
in the last case, to these seeds having germinated rather sooner than
those from the crossed plants; but at the close of the season the
tallest of the self-fertilised plants from the crossed plants was 30
inches, whilst the tallest of the self-fertilised from the
self-fertilised was 29 3/8 inches in height.
From the various facts now given we see that plants derived from a cross
between two varieties of the sweet-pea, which differ in no respect
except in the colour of their flowers, exceed considerably in height the
offspring from self-fertilised plants, both in the first and second
generations. The crossed plants also transmit their superiority in
height and vigour to their self-fertilised offspring.
Pisum sativum.
The common pea is perfectly fertile when its flowers are protected from
the visits of insects; I ascertained this with two or three different
varieties, as did Dr. Ogle with another. But the flowers are likewise
adapted for cross-fertilisation; Mr. Farrer specifies the following
points, namely: "The open blossom displaying itself in the most
attractive and convenient position for insects; the conspicuous
vexillum; the wings forming an alighting place; the attachment of the
wings to the keel, by which any body pressing on the former must press
down the latter; the staminal tube enclosing nectar, and affording by
means of its partially free stamen with apertures on each side of its
base an open passage to an insect seeking the nectar; the moist and
sticky pollen placed just where it will be swept out of the apex of the
keel against the entering insect; the stiff elastic style so placed that
on a pressure being applied to the keel it will be pushed upwards out of
the keel; the hairs on the style placed on that side of the style only
on which there is space for the pollen, and in such a direction as to
sweep it out; and the stigma so placed as to meet an entering
insect,--all these become correlated parts of one elaborate mechanism,
if we suppose that the fertilisation of these flowers is effected by the
carriage of pollen from one to the other.
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