Tabernaemontana echinata (Apocynaceae).—­Quite sterile.

Petunia violacea (Solanaceae).—­Quite sterile, as far as I have observed.

Solanum tuberosum (Solanaceae).—­Tinzmann says (’Gardeners’ Chronicle’ 1846 page 183) that some varieties are quite sterile unless fertilised by pollen from another variety.

Primula scotica (Primulaceae).—­A non-dimorphic species, which is fertile with its own pollen, but is extremely sterile if insects are excluded.  J. Scott in ‘Journal of the Linnean Society Botany’ volume 8 1864 page 119.

Cortusa matthioli (Primulaceae).—­Protected plants completely sterile; artificially self-fertilised flowers perfectly fertile.  J. Scott ibid. page 84.

Cyclamen persicum (Primulaceae).—­During one season several covered-up plants did not produce a single seed.

Borago officinalis (Boraginaceae).—­Protected plants produced about half as many seeds as the unprotected.

Salvia tenori (Labiatae).—­Quite sterile; but two or three flowers on the summits of three of the spikes, which touched the net when the wind blew, produced a few seeds.  This sterility was not due to the injurious effects of the net, for I fertilised five flowers with pollen from an adjoining plant, and these all yielded fine seeds.  I removed the net, whilst one little branch still bore a few not completely faded flowers, and these were visited by bees and yielded seeds.

Salvia coccinea.—­Some covered-up plants produced a good many fruits, but not, I think, half as many as did the uncovered plants; twenty-eight of the fruits spontaneously produced by the protected plant contained on an average only 1.45 seeds, whilst some artificially self-fertilised fruits on the same plant contained more than twice as many, namely 3.3 seeds.

Bignonia (unnamed species) (Bignoniaceae).—­Quite sterile:  see my account of self-sterile plants.

Digitalis purpurea (Scrophulariaceae).—­Extremely sterile, only a few poor capsules being produced.

Linaria vulgaris (Scrophulariaceae).—­Extremely sterile.

Antirrhinum majus, red var. (Scrophulariaceae).—­Fifty pods gathered from a large plant under a net contained 9.8 grains weight of seeds; but many (unfortunately not counted) of the fifty pods contained no seeds.  Fifty pods on a plant fully exposed to the visits of humble-bees contained 23.1 grains weight of seed, that is, more than twice the weight; but in this case again, several of the fifty pods contained no seeds.

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.