Antirrhinum majus (peloric var.).—­This variety is quite fertile when artificially fertilised with its own pollen, but is utterly sterile when left to itself and uncovered, as humble-bees cannot crawl into the narrow tubular flowers.

Verbascum phoeniceum (Scrophulariaceae).—­Quite sterile.  See my account of self-sterile plants.

Verbascum nigrum.—­Quite sterile.  See my account of self-sterile plants.

Campanula carpathica (Lobeliaceae).—­Quite sterile.

Lobelia ramosa (Lobeliaceae).—­Quite sterile.

Lobelia fulgens.—­This plant is never visited in my garden by bees, and is quite sterile; but in a nursery-garden at a few miles’ distance I saw humble-bees visiting the flowers, and they produced some capsules.

Isotoma (a white-flowered var.) (Lobeliaceae).—­Five plants left unprotected in my greenhouse produced twenty-four fine capsules, containing altogether 12.2 grains weight of seed, and thirteen other very poor capsules, which were rejected.  Five plants protected from insects, but otherwise exposed to the same conditions as the above plants, produced sixteen fine capsules, and twenty other very poor and rejected ones.  The sixteen fine capsules contained seeds by weight in such proportion that twenty-four would have yielded 4.66 grains.  So that the unprotected plants produced nearly thrice as many seeds by weight as the protected plants.

Leschenaultia formosa (Goodeniaceae).—­Quite sterile.  My experiments on this plant, showing the necessity of insect aid, are given in the ‘Gardeners’ Chronicle’ 1871 page 1166.

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.

List of 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.