3. GESNERIACEAE.--Gesneria pendulina.

In Gesneria the several parts of the flower are arranged on nearly the same plan as in Digitalis, and most or all of the species are dichogamous. (3/11. Dr. Ogle 'Popular Science Review' January 1870 page 51.) Plants were raised from seed sent me by Fritz Muller from South Brazil. Seven flowers were crossed with pollen from a distinct plant, and produced seven capsules containing by weight 3.01 grains of seeds. Seven flowers on the same plants were fertilised with their own pollen, and their seven capsules contained exactly the same weight of seeds. Germinating seeds were planted on opposite sides of four pots, and when fully grown measured to the tips of their leaves.

TABLE 3/26. Gesneria pendulina.

Heights of Plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 42 2/8 : 39. Pot 1 : 24 4/8 : 27 3/8.

Pot 2 : 33 : 30 6/8. Pot 2 : 27 : 19 2/8.

Pot 3 : 33 4/8 : 31 7/8. Pot 3 : 29 4/8 : 28 6/8.

Pot 4 : 30 6/8 : 29 6/8. Pot 4 : 36 : 26 3/8.

Total : 256.50 : 233.13.

The average height of the eight crossed plants is 32.06 inches, and that of the eight self-fertilised plants 29.14; or as 100 to 90.

4. LABIATAE.--Salvia coccinea. (3/12. The admirable mechanical adaptations in this genus for favouring or ensuring cross-fertilisation, have been fully described by Sprengel, Hildebrand, Delpino, H. Muller, Ogle, and others, in their several works.)

This species, unlike most of the others in the same genus, yields a good many seeds when insects are excluded. I gathered ninety-eight capsules produced by flowers spontaneously self-fertilised under a net, and they contained on an average 1.45 seeds, whilst flowers artificially fertilised with their own pollen, in which case the stigma will have received plenty of pollen, yielded on an average 3.3 seeds, or more than twice as many. Twenty flowers were crossed with pollen from a distinct plant, and twenty-six were self-fertilised. There was no great difference in the proportional number of flowers which produced capsules by these two processes, or in the number of the contained seeds, or in the weight of an equal number of seeds.

Seeds of both kinds were sown rather thickly on opposite sides of three pots. When the seedlings were about 3 inches in height, the crossed showed a slight advantage over the self-fertilised. When two-thirds grown, the two tallest plants on each side of each pot were measured; the crossed averaged 16.37 inches, and the self-fertilised 11.75 in height; or as 100 to 71. When the plants were fully grown and had done flowering, the two tallest plants on each side were again measured, with the results shown in Table 3/27.

TABLE 3/27. Salvia coccinea.

Heights of Plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 32 6/8 : 25. Pot 1 : 20 : 18 6/8.

Pot 2 : 32 3/8 : 20 6/8. Pot 2 : 24 4/8 : 19 4/8.

Pot 3 : 29 4/8 : 25. Pot 3 : 28 : 18.

Total : 167.13 : 127.00.

It may be here seen that each of the six tallest crossed plants exceeds in height its self-fertilised opponent; the former averaged 27.85 inches, whilst the six tallest self-fertilised plants averaged 21.16 inches; or as 100 to 76. In all three pots the first plant which flowered was a crossed one. All the crossed plants together produced 409 flowers, whilst all the self-fertilised together produced only 232 flowers; or as 100 to 57. So that the crossed plants in this respect were far more productive than the self-fertilised.

Origanum vulgare.

This plant exists, according to H. Muller, under two forms; one hermaphrodite and strongly proterandrous, so that it is almost certain to be fertilised by pollen from another flower; the other form is exclusively female, has a smaller corolla, and must of course be fertilised by pollen from a distinct plant in order to yield any seeds. The plants on which I experimented were hermaphrodites; they had been cultivated for a long period as a pot-herb in my kitchen garden, and were, like so many long-cultivated plants, extremely sterile.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 47

19th Century English Literature

Charles Darwin

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