CHAPTER V. GERANIACEAE, LEGUMINOSAE, ONAGRACEAE, ETC.
Pelargonium zonale, a cross between plants propagated by cuttings does
no good.
Tropaeolum minus.
Limnanthes douglasii.
Lupinus luteus and pilosus.
Phaseolus multiflorus and vulgaris.
Lathyrus odoratus, varieties of, never naturally intercross in England.
Pisum sativum, varieties of, rarely intercross, but a cross between them
highly beneficial.
Sarothamnus scoparius, wonderful effects of a cross.
Ononis minutissima, cleistogene flowers of.
Summary on the Leguminosae.
Clarkia elegans.
Bartonia aurea.
Passiflora gracilis.
Apium petroselinum.
Scabiosa atropurpurea.
Lactuca sativa.
Specularia speculum.
Lobelia ramosa, advantages of a cross during two generations.
Lobelia fulgens.
Nemophila insignis, great advantages of a cross.
Borago officinalis.
Nolana prostrata.
13. GERANIACEAE.—Pelargonium zonale.
This plant, as a general rule, is strongly proterandrous, and is therefore adapted for cross-fertilisation by the aid of insects. (5/1. Mr. J. Denny, a great raiser of new varieties of pelargoniums, after stating that this species is proterandrous, adds ‘The Florist and Pomologist’ January 1872 page 11, “there are some varieties, especially those with petals of a pink colour, or which possess a weakly constitution, where the pistil expands as soon as or even before the pollen-bag bursts, and in which also the pistil is frequently short, so when it expands it is smothered as it were by the bursting anthers; these varieties are great seeders, each pip being fertilised by its own pollen. I would instance Christine as an example of this fact.” We have here an interesting case of variability in an important functional point.) Some flowers on a common scarlet variety were self-fertilised, and other flowers were crossed with pollen from another plant; but no sooner had I done so, than I remembered that these plants had been propagated by cuttings from the same stock, and were therefore parts in a strict sense of the same individual. Nevertheless, having made the cross I resolved to save the seeds, which, after germinating on sand, were planted on the opposite sides of three pots. In one pot the quasi-crossed plant was very soon and ever afterwards taller and finer than the self-fertilised. In the two other pots the seedlings on both sides were for a time exactly equal; but when the self-fertilised plants were about 10 inches in height, they surpassed their antagonists by a little, and ever afterwards showed a more decided and increasing advantage; so that the self-fertilised plants, taken altogether, were somewhat superior to the quasi-crossed plants. In this case, as in that of the Origanum, if individuals which have been asexually propagated from the same stock, and which have been long subjected to the same conditions, are crossed, no advantage whatever is gained.
Several flowers on another plant of the same variety were fertilised with pollen from the younger flowers on the same plant, so as to avoid using the old and long-shed pollen from the same flower, as I thought that this latter might be less efficient than fresh pollen. Other flowers on the same plant were crossed with fresh pollen from a plant which, although closely similar, was known to have arisen as a distinct seedling. The self-fertilised seeds germinated rather before the others; but as soon as I got equal pairs they were planted on the opposite sides of four pots.
TABLE 5/49. Pelargonium zonale.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 22 3/8 : 25 5/8. Pot 1 : 19 6/8 : 12 4/8.
Pot 2 : 15 : 19 6/8. Pot 2 : 12 2/8 : 22 3/8.
Pot 3 : 30 5/8 : 19 4/8. Pot 3 : 18 4/8 : 7 4/8.
Pot 4 : 38 : 9 1/8.
Total : 156.50 : 116.38.
When the two lots of seedlings were between 4 and 5 inches in height they were equal, excepting in Pot 4, in which the crossed plant was much the tallest. When between 11 and 14 inches in height, they were measured to the tips of their uppermost leaves; the crossed averaged 13.46, and the self-fertilised 11.07 inches in height, or as 100 to 82. Five months later they were again measured in the same manner, and the results are given in Table 5/49.
The seven crossed plants now averaged 22.35, and the seven self-fertilised 16.62 inches in height, or as 100 to 74. But from the great inequality of the several plants, the result is less trustworthy than in most other cases. In Pot 2 the two self-fertilised plants always had an advantage, except whilst quite young over the two crossed plants.
As I wished to ascertain how these plants would behave during a second growth, they were cut down close to the ground whilst growing freely. The crossed plants now showed their superiority in another way, for only one out of the seven was killed by the operation, whilst three of the self-fertilised plants never recovered. There was, therefore, no use in keeping any of the plants excepting those in Pots 1 and 3; and in the following year the crossed plants in these two pots showed during their second growth nearly the same relative superiority over the self-fertilised plants as before.
Tropaeolum minus.
The flowers are proterandrous, and are manifestly adapted for cross-fertilisation by insects, as shown by Sprengel and Delpino. Twelve flowers on some plants growing out of doors were crossed with pollen from a distinct plant and produced eleven capsules, containing altogether twenty-four good seeds. Eighteen flowers were fertilised with their own pollen and produced only eleven capsules, containing twenty-two good seeds; so that a much larger proportion of the crossed than of the self-fertilised flowers produced capsules, and the crossed capsules contained rather more seed than the self-fertilised in the ratio of 100 to 92. The seeds from the self-fertilised capsules were however the heavier of the two, in the ratio of 100 to 87.
Seeds in an equal state of germination were planted on the opposite sides of four pots, but only the two tallest plants on each side of each pot were measured to the tops of their stems. The pots were placed in the greenhouse, and the plants trained up sticks, so that they ascended to an unusual height. In three of the pots the crossed plants flowered first, but in the fourth at the same time with the self-fertilised. When the seedlings were between 6 and 7 inches in height, the crossed began to show a slight advantage over their opponents. When grown to a considerable height the eight tallest crossed plants averaged 44.43, and the eight tallest self-fertilised plants 37.34 inches, or as 100 to 84. When their growth was completed they were again measured, as shown in Table 5/50.
TABLE 5/50. Tropaeolum minus.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 65 : 31. Pot 1 : 50 : 45.
Pot 2 : 69 : 42. Pot 2 : 35 : 45.
Pot 3 : 70 : 50 4/8. Pot 3 : 59 4/8 : 55 4/8.
Pot 4 : 61 4/8 : 37 4/8. Pot 4 : 57 4/8 : 61 4/8.
Total : 467.5 : 368.0.
The eight tallest crossed plants now averaged 58.43, and the eight tallest self-fertilised plants 46 inches in height, or as 100 to 79.
There was also a great difference in the fertility of the two lots which were left uncovered in the greenhouse. On the 17th of September the capsules from all the plants were gathered, and the seeds counted. The crossed plants yielded 243, whilst the same number of self-fertilised plants yielded only 155 seeds, or as 100 to 64.
Limnanthes douglasii.
Several flowers were crossed and self-fertilised in the usual manner, but there was no marked difference in the number of seeds which they yielded. A vast number of spontaneously self-fertilised capsules were also produced under the net. Seedlings were raised in five pots from the above seeds, and when the crossed were about 3 inches in height they showed a slight advantage over the self-fertilised. When double this height, the sixteen crossed and sixteen self-fertilised plants were measured to the tips of their leaves; the former averaged 7.3 inches, and the self-fertilised 6.07 inches in height, or as 100 to 83. In all the pots, excepting 4, a crossed plant flowered before any one of the self-fertilised plants. The plants, when fully grown, were again measured to the summits of their ripe capsules, with the result in Table 5/51.
TABLE 5/51. Limnanthes douglasii.
Heights of plants to the summits of their ripe capsules, measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 17 7/8 : 15 1/8. Pot 1 : 17 6/8 : 16 4/8. Pot 1 : 13 : 11.
Pot 2 : 20 : 14 4/8. Pot 2 : 22 : 15 6/8. Pot 2 : 21 : 16 1/8. Pot 2 : 18 4/8 : 17.
Pot 3 : 15 6/8 : 11 4/8. Pot 3 : 17 2/8 : 10 4/8. Pot 3 : 14 : 0.
Pot 4 : 20 4/8 : 13 4/8. Pot 4 : 14 : 13. Pot 4 : 18 : 12 2/8.
Pot 5 : 17 : 14 2/8. Pot 5 : 18 5/8 : 14 1/8. Pot 5 : 14 2/8 : 12 5/8.
Total : 279.50 : 207.75.
The sixteen crossed plants now averaged 17.46, and the fifteen (for one had died) self-fertilised plants 13.85 inches in height, or as 100 to 79. Mr. Galton considers that a higher ratio would be fairer, namely, 100 to 76. He made a graphical representation of the above measurements, and adds the words “very good” to the curvature thus formed. Both lots of plants produced an abundance of seed-capsules, and, as far as could be judged by the eye, there was no difference in their fertility.]