Senecio cruentus (Compositae).—Quite sterile: see my account of self-sterile plants.
Heterocentron mexicanum (Malastomaceae).—Quite sterile; but this species and the following members of the group produce plenty of seed when artificially self-fertilised.
Rhexia glandulosa (Melastomaceae).—Set spontaneously only two or three capsules.
Centradenia floribunda (Melastomaceae).—During some years produced spontaneously two or three capsules, sometimes none.
Pleroma (unnamed species from Kew) (Melastomaceae).—During some years produced spontaneously two or three capsules, sometimes none.
Monochaetum ensiferum (Melastomaceae).—During some years produced spontaneously two or three capsules, sometimes none.
Hedychium (unnamed species) (Marantaceae).—Almost self-sterile without aid.
Orchideae.—An immense proportion of the species sterile, if insects are excluded.
PLANTS, WHICH WHEN PROTECTED FROM INSECTS ARE EITHER QUITE FERTILE, OR YIELD MORE THAN HALF THE NUMBER OF SEEDS PRODUCED BY UNPROTECTED PLANTS.
Passiflora gracilis (Passifloraceae).—Produces many fruits, but these contain fewer seeds than fruits from intercrossed flowers.