It is a more probable view that the papillae, which render the stigma
of the long-styled form of various species rough, serve to entangle effectually
the large-sized pollen-grains brought by insects from the short-styled form,
thus ensuring its legitimate fertilisation. This view is supported by the fact
that the pollen-grains from the two forms of eight species in Table 6.34 hardly
differ in diameter, and the papillae on their stigmas do not differ in length.
The species which are at present positively or almost positively known to be
heterostyled belong, as shown in Table 6.35, to 38 genera, widely distributed
throughout the world. These genera are included in fourteen Families, most of
which are very distinct from one another, for they belong to nine of the several
great Series, into which phanerogamic plants have been divided by Bentham and
Hooker.
TABLE 6.35. List of genera including heterostyled species.
DICOTYLEDONS.
HYPERICINEAE:
Cratoxylon.
ERYTHROXYLEAE:
Erythroxylum.
Sethia.
GERANIACEAE:
Linum.
Oxalis.
LYTHRACEAE:
Lythrum.
Neseae.
RUBIACEAE:
Cinchona.
Bouvardia.
Manettia.
Hedyotis.
Oldenlandia.
Houstonia.
Coccocypselum.
Lipostoma.
Knoxia.
Faramea.
Psychotria.
Rudgea.
Suteria.
Mitchella.
Diodia.
Borreria.
Spermacoce.
PRIMULACEAE:
Primula.
Hottonia.
Androsace.
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