5. Acanthaceae.—Thunbergia alata.
It appears from Hildebrand’s description (’Botanische Zeitung’ 1867 page 285) that the conspicuous flowers of this plant are adapted for cross-fertilisation. Seedlings were twice raised from purchased seed; but during the early summer, when first experimented on, they were extremely sterile, many of the anthers containing hardly any pollen. Nevertheless, during the autumn these same plants spontaneously produced a good many seeds. Twenty-six flowers during the two years were crossed with pollen from a distinct plant, but they yielded only eleven capsules; and these contained very few seeds! Twenty-eight flowers were fertilised with pollen from the same flower, and these yielded only ten capsules, which, however, contained rather more seed than the crossed capsules. Eight pairs of germinating seeds were planted on opposite sides of five pots; and exactly half the crossed and half the self-fertilised plants exceeded their opponents in height. Two of the self-fertilised plants died young, before they were measured, and their crossed opponents were thrown away. The six remaining pairs of these grew very unequally, some, both of the crossed and self-fertilised plants, being more than twice as tall as the others. The average height of the crossed plants was 60 inches, and that of the self-fertilised plants 65 inches, or as 100 to 108. A cross, therefore, between distinct individuals here appears to do no good; but this result deduced from so few plants in a very sterile condition and growing very unequally, obviously cannot be trusted.]
CRUCIFERAE, PAPAVERACEAE, RESEDACEAE, ETC.
Brassica oleracea, crossed and self-fertilised plants.
Great effect of a cross with a fresh stock on the weight of the
Eschscholtzia californica, seedlings from a cross with a fresh stock not
more vigorous, but more fertile than the self-fertilised seedlings.
Reseda lutea and odorata, many individuals sterile with their own pollen.
Viola tricolor, wonderful effects of a cross.
Viscaria oculata, crossed plants hardly taller, but more fertile than
Dianthus caryophyllus, crossed and self-fertilised plants compared for
Great effects of a cross with a fresh stock.
Uniform colour of the flowers on the self-fertilised plants.