Antirrhinum majus (white var., with a pink mouth to the corolla).--Fifty pods, of which only a very few were empty, on a covered-up plant contained 20 grains weight of seed; so that this variety seems to be much more self-fertile than the previous one. With Dr. W. Ogle ('Popular Science Review' January 1870 page 52) a plant of this species was much more sterile when protected from insects than with me, for it produced only two small capsules. As showing the efficiency of bees, I may add that Mr. Crocker castrated some young flowers and left them uncovered; and these produced as many seeds as the unmutilated flowers.
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.
Brassica oleracea (Cruciferae).--Produces many capsules, but these generally not so rich in seed as those on uncovered plants.
Raphanus sativus (Cruciferae).--Half of a large branching plant was covered by a net, and was as thickly covered with capsules as the other and unprotected half; but twenty of the capsules on the latter contained on an average 3.5 seeds, whilst twenty of the protected capsules contained only 1.85 seeds, that is, only a little more than half the number. This plant might perhaps have been more properly included in the former list.
Iberis umbellata (Cruciferae).--Highly fertile.
Iberis amara.--Highly fertile.
Reseda odorata and lutea (Resedaceae).--Certain individuals completely self-fertile.