Thirdly and lastly, these hybrids offer an excellent
illustration of a statement made by that admirable observer Gartner, namely,
that although plants which can be crossed with ease generally produce fairly
fertile offspring, yet well-pronounced exceptions to this rule occur; and here
we have two species of Verbascum which evidently cross with the greatest ease,
but produce hybrids which are excessively sterile.
CHAPTER III. HETEROSTYLED DIMORPHIC PLANTS--continued.
Linum grandiflorum, long-styled form utterly sterile with own-form pollen.
Linum perenne, torsion of the pistils in the long-styled form alone.
Homostyled species of Linum.
Pulmonaria officinalis, singular difference in self-fertility between the
English and German long-styled plants.
Pulmonaria angustifolia shown to be a distinct species, long-styled form
completely self-sterile.
Polygonum fagopyrum.
Various other heterostyled genera.
Rubiaceae.
Mitchella repens, fertility of the flowers in pairs.
Houstonia.
Faramea, remarkable difference in the pollen-grains of the two forms; torsion of
the stamens in the short-styled form alone; development not as yet perfect.
The heterostyled structure in the several Rubiaceous genera not due to descent
in common.
(FIGURE 3.4. Linum grandiflorum.
Left: Long-styled form.
Right: Short-styled form.
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