Mr. Scott has given a still more striking illustration of the same fact:
he crossed Primula auricula with pollen of four other species (P. palinuri,
viscosa, hirsuta, and verticillata), and these hybrid unions yielded a larger
average number of seeds than did P. auricula when fertilised illegitimately with
its own-form pollen. (1/7. 'Journal of the Linnean Society Botany' volume 8 1864
page 93.)
The benefit which heterostyled dimorphic plants derive from the existence of the
two forms is sufficiently obvious, namely, the intercrossing of distinct plants
being thus ensured. (1/8. I have shown in my work on the 'Effects of Cross and
Self-fertilisation' how greatly the offspring from intercrossed plants profit in
height, vigour, and fertility.) Nothing can be better adapted for this end than
the relative positions of the anthers and stigmas in the two forms, as shown in
Figure 1.2; but to this whole subject I shall recur. No doubt pollen will
occasionally be placed by insects or fall on the stigma of the same flower; and
if cross-fertilisation fails, such self-fertilisation will be advantageous to
the plant, as it will thus be saved from complete barrenness. But the advantage
is not so great as might at first be thought, for the seedlings from
illegitimate unions do not generally consist of both forms, but all belong to
the parent form; they are, moreover, in some degree weakly in constitution, as
will be shown in a future chapter.
Pages:
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62