The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 32

These two lots of seeds were sown on opposite sides of two large pots; but I succeeded in raising only four pairs of equal age. When the seedlings on both sides were about 8 inches in height they were equal.

When in full flower they were measured, as follows:--

TABLE 5/74. Borago officinalis.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 19 : 13 4/8.

Pot 1 : 21 : 18 6/8.

Pot 1 : 16 4/8 : 20 2/8.

Pot 2 : 26 2/8 : 32 2/8.

Total : 82.75 : 84.75.

The average height of the four crossed plants is here 20.68, and that of the four self-fertilised 21.18 inches; or as 100 to 102. The self-fertilised plants thus exceeded the crossed in height by a little; but this was entirely due to the tallness of one of the self-fertilised.

The crossed plants in both pots flowered before the self-fertilised.

Therefore I believe if more plants had been raised, the result would have been different. I regret that I did not attend to the fertility of the two lots.

24. NOLANACEAE.--Nolana prostrata.

In some of the flowers the stamens are considerably shorter than the pistil, in others equal to it in length. I suspected, therefore, but erroneously as it proved, that this plant was dimorphic, like Primula, Linum, etc., and in the year 1862 twelve plants, covered by a net in the greenhouse, were subjected to trial. The spontaneously self-fertilised flowers yielded 64 grains weight of seeds, but the product of fourteen artificially crossed flowers is here included, which falsely increases the weight of the self-fertilised seeds. Nine uncovered plants, the flowers of which were eagerly visited by bees for their pollen and were no doubt intercrossed by them, produced 79 grains weight of seeds: therefore twelve plants thus treated would have yielded 105 grains. Thus the seeds produced by the flowers on an equal number of plants, when crossed by bees, and spontaneously self-fertilised (the product of fourteen artificially crossed flowers being, however, included in the latter) were in weight as 100 to 61.

In the summer of 1867 the trial was repeated; thirty flowers were crossed with pollen from a distinct plant and produced twenty-seven capsules, each containing five seeds. Thirty-two flowers were fertilised with their own pollen, and produced only six capsules, each with five seeds. So that the crossed and self-fertilised capsules contained the same number of seeds, though many more capsules were produced by the cross-fertilised than by the self-fertilised flowers, in the ratio of 100 to 21.

An equal number of seeds of both lots were weighed, and the crossed seeds were to the self-fertilised in weight as 100 to 82. Therefore a cross increases the number of capsules produced and the weight of the seeds, but not the number of seeds in each capsule.

These two lots of seeds, after germinating on sand, were planted on the opposite sides of three pots. The seedlings when from 6 to 7 inches in height were equal. The plants were measured when fully grown, but their heights were so unequal in the several pots, that the result cannot be fully trusted.

TABLE 5/75. Nolana prostrata.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 8 4/8 : 4 2/8.

Pot 1 : 6 4/8 : 7 4/8.

Pot 2 : 10 4/8 : 14 4/8.

Pot 2 : 18 : 18.

Pot 3 : 20 2/8 : 22 6/8.

Total : 63.75 : 67.00.

The five crossed plants average 12.75, and the five self-fertilised 13.4 inches in height; or as 100 to 105.

CHAPTER VI.

SOLANACEAE, PRIMULACEAE, POLYGONEAE, ETC.

Petunia violacea, crossed and self-fertilised plants compared for four generations.

Effects of a cross with a fresh stock.

Uniform colour of the flowers on the self-fertilised plants of the fourth generation.

Nicotiana tabac.u.m, crossed and self-fertilised plants of equal height.

Great effects of a cross with a distinct sub-variety on the height, but not on the fertility, of the offspring.

Cyclamen persic.u.m, crossed seedlings greatly superior to the self-fertilised.

Anagallis collina.

Primula veris.

Equal-styled variety of Primula veris, fertility of, greatly increased by a cross with a fresh stock.

f.a.gopyrum esculentum.

Beta vulgaris.

Canna warscewiczi, crossed and self-fertilised plants of equal height.

Zea mays.

Phalaris canariensis.

25. SOLANACEAE. Petunia violacea.

DINGY PURPLE VARIETY.

The flowers of this plant are so seldom visited during the day by insects in this country, that I have never seen an instance; but my gardener, on whom I can rely, once saw some humble-bees at work. Mr.

Meehan says, that in the United States bees bore through the corolla for the nectar, and adds that their "fertilisation is carried on by night-moths." (6/1. 'Proceedings of the Academy of Natural Science of Philadelphia' August 2, 1870 page 90.)

In France M. Naudin, after castrating a large number of flowers whilst in bud, left them exposed to the visits of insects, and about a quarter produced capsules (6/2. 'Annales des Sc. Nat.' 4th series Bot. Tome 9 cah. 5); but I am convinced that a much larger proportion of flowers in my garden are cross-fertilised by insects, for protected flowers with their own pollen placed on the stigma never yielded nearly a full complement of seed; whilst those left uncovered produced fine capsules, showing that pollen from other plants must have been brought to them, probably by moths. Plants growing vigorously and flowering in pots in the greenhouse, never yielded a single capsule; and this may be attributed, at least in chief part, to the exclusion of moths.

Six flowers on a plant covered by a net were crossed with pollen from a distinct plant and produced six capsules, containing by weight 4.44 grains of seed. Six other flowers were fertilised with their own pollen and produced only three capsules, containing only 1.49 grains weight of seed. From this it follows that an equal number of crossed and self-fertilised capsules would have contained seeds by weight as 100 to 67. I should not have thought the proportional contents of so few capsules worth giving, had not nearly the same result been confirmed by several subsequent trials.

Seeds of the two lots were placed on sand, and many of the self-fertilised seeds germinated before the crossed, and were rejected.

Several pairs in an equal state of germination were planted on the opposite sides of Pots 1 and 2; but only the tallest plant on each side was measured. Seeds were also sown thickly on the two sides of a large pot (3), the seedlings being afterwards thinned, so that an equal number was left on each side; the three tallest on each side being measured.

The pots were kept in the greenhouse, and the plants were trained up sticks. For some time the young crossed plants had no advantage in height over the self-fertilised; but their leaves were larger. When fully grown and in flower the plants were measured, as follows:--

TABLE 6/76. Petunia violacea (first generation).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.