CHAPTER III. SCROPHULARIACEAE, GESNERIACEAE, LABIATAE, ETC.
Mimulus luteus; height, vigour, and fertility of the crossed and
self-fertilised plants of the first four generations.
Appearance of a new, tall, and highly self-fertile variety.
Offspring from a cross between self-fertilised plants.
Effects of a cross with a fresh stock.
Effects of crossing flowers on the same plant.
Summary on Mimulus luteus.
Digitalis purpurea, superiority of the crossed plants.
Effects of crossing flowers on the same plant.
Calceolaria.
Linaria vulgaris.
Verbascum thapsus.
Vandellia nummularifolia.
Cleistogene flowers.
Gesneria pendulina.
Salvia coccinea.
Origanum vulgare, great increase of the crossed plants by stolons.
Thunbergia alata.
In the family of the Scrophulariaceae I experimented on species in the six following genera: Mimulus, Digitalis, Calceolaria, Linaria, Verbascum, and Vandellia.
[3/2. SCROPHULARIACEAE.—Mimulus luteus.
The plants which I raised from purchased seed varied greatly in the colour of their flowers, so that hardly two individuals were quite alike; the corolla being of all shades of yellow, with the most diversified blotches of purple, crimson, orange, and coppery brown. But these plants differed in no other respect. (3/1. I sent several specimens with variously coloured flowers to Kew, and Dr. Hooker informs me that they all consisted of Mimulus luteus. The flowers with much red have been named by horticulturists as var. Youngiana.) The flowers are evidently well adapted for fertilisation by the agency of insects; and in the case of a closely allied species, Mimulus rosea, I have watched bees entering the flowers, thus getting their backs well dusted with pollen; and when they entered another flower the pollen was licked off their backs by the two-lipped stigma, the lips of which are irritable and close like a forceps on the pollen-grains. If no pollen is enclosed between the lips, these open again after a time. Mr. Kitchener has ingeniously explained the use of these movements, namely, to prevent the self-fertilisation of the flower. (3/2. ‘A Year’s Botany’ 1874 page 118.) If a bee with no pollen on its back enters a flower it touches the stigma, which quickly closes, and when the bee retires dusted with pollen, it can leave none on the stigma of the same flower. But as soon as it enters any other flower, plenty of pollen is left on the stigma, which will be thus cross-fertilised. Nevertheless, if insects are excluded, the flowers fertilise themselves perfectly and produce plenty of seed; but I did not ascertain whether this is effected by the stamens increasing in length with advancing age, or by the bending down of the pistil. The chief interest in my experiments on the present species, lies in the appearance in the fourth self-fertilised generation of a variety which bore large peculiarly-coloured flowers, and grew to a greater height than the other varieties; it likewise became more highly self-fertile, so that this variety resembles the plant named Hero, which appeared in the sixth self-fertilised generation of Ipomoea.
Some flowers on one of the plants raised from the purchased seeds were fertilised with their own pollen; and others on the same plant were crossed with pollen from a distinct plant. The seeds from twelve capsules thus produced were placed in separate watch-glasses for comparison; and those from the six crossed capsules appeared to the eye hardly more numerous than those from the six self-fertilised capsules. But when the seeds were weighed, those from the crossed capsules amounted to 1.02 grain, whilst those from the self-fertilised capsules were only .81 grain; so that the former were either heavier or more numerous than the latter, in the ratio of 100 to 79.