The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 31

Pot 6 : 26 1/8 : 37.

Pot 6 : 25 : 35.

Pot 7 : 30 6/8 : 27 2/8.

Pot 7 : 30 3/8 : 19 2/8.

Pot 7 : 29 2/8 : 21.

Pot 8 : 39 3/8 : 23 1/8.

Pot 8 : 37 2/8 : 23 4/8.

Pot 8 : 36 : 25 4/8.

Pot 8 : 36 : 25 1/8.

Pot 9 : 33 3/8 : 19 3/8.

Pot 9 : 25 : 16 3/8.

Pot 9 : 25 3/8 : 19.

Pot 9 : 21 7/8 : 18 6/8.

Total : 1014.00 : 921.63.

I determined on this occasion to avoid the error of using pollen of not quite equal maturity for crossing and self-fertilisation; so that I squeezed pollen out of the conjoined anthers of young flowers for both operations. Several flowers on the crossed plant in Pot 1 in Table 5/70 were again crossed with pollen from a distinct plant. Several other flowers on the self-fertilised plant in the same pot were again self-fertilised with pollen from the anthers of other flowers on the SAME PLANT. Therefore the degree of self-fertilisation was not quite so close as in the last generation, in which pollen from the SAME FLOWER, kept in paper, was used. These two lots of seeds were thinly sown on opposite sides of nine pots; and the young seedlings were thinned, an equal number of nearly as possible the same age being left on the two sides. In the spring of the following year (1870), when the seedlings had grown to a considerable size, they were measured to the tips of their leaves; and the twenty-three crossed plants averaged 14.04 inches in height, whilst the twenty-three self-fertilised seedlings were 13.54 inches; or as 100 to 96.

In the summer of the same year several of these plants flowered, the crossed and self-fertilised plants flowering almost simultaneously, and all the flower-stems were measured. Those produced by eleven of the crossed plants averaged 30.71 inches, and those by nine of the self-fertilised plants 29.43 inches in height; or as 100 to 96.

The plants in these nine pots, after they had flowered, were repotted without being disturbed in much larger pots; and in the following year, 1871, all flowered freely; but they had grown into such an entangled ma.s.s, that the separate plants on each side could no longer be distinguished. Accordingly three or four of the tallest flower-stems on each side of each pot were measured; and the measurements in Table 5/71 are, I think, more trustworthy than the previous ones, from being more numerous, and from the plants being well established and growing vigorously.

The average height of the thirty-four tallest flower-stems on the twenty-three crossed plants is 29.82 inches, and that of the same number of flower-stems on the same number of self-fertilised plants is 27.10 inches, or as 100 to 91. So that the crossed plants now showed a decided advantage over their self-fertilised opponents.

22. POLEMONIACEAE.--Nemophila insignis.

Twelve flowers were crossed with pollen from a distinct plant, but produced only six capsules, containing on an average 18.3 seeds.

Eighteen flowers were fertilised with their own pollen and produced ten capsules, containing on an average 12.7 seeds, so that the seeds per capsule were as 100 to 69. (5/25. Several species of Polemoniaceae are known to be proterandrous, but I did not attend to this point in Nemophila. Verlot says 'Des Varietes' 1865 page 66, that varieties growing near one another spontaneously intercross.) The crossed seeds weighed a little less than an equal number of self-fertilised seeds, in the proportion of 100 to 105; but this was clearly due to some of the self-fertilised capsules containing very few seeds, and these were much bulkier than the others, from having been better nourished. A subsequent comparison of the number of seeds in a few capsules did not show so great a superiority on the side of the crossed capsules as in the present case.

The seeds were placed on sand, and after germinating were planted in pairs on the opposite sides of five pots, which were kept in the greenhouse. When the seedlings were from 2 to 3 inches in height, most of the crossed had a slight advantage over the self-fertilised. The plants were trained up sticks, and thus grew to a considerable height.

In four out of the five pots a crossed plant flowered before any one of the self-fertilised. The plants were first measured to the tips of their leaves, before they had flowered and when the crossed were under a foot in height. The twelve crossed plants averaged 11.1 inches in height, whilst the twelve self-fertilised were less than half of this height, namely, 5.45; or as 100 to 49. Before the plants had grown to their full height, two of the self-fertilised died, and as I feared that this might happen with others, they were again measured to the tops of their stems, as shown in Table 5/72.

TABLE 5/72. Nemophila insignis; 0 means that the plant died.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 32 4/8 : 21 2/8.

Pot 2 : 34 4/8 : 23 5/8.

Pot 3 : 33 1/8 : 19.

Pot 3 : 22 2/8 : 7 2/8.

Pot 3 : 29 : 17 4/8.

Pot 4 : 35 4/8 : 10 4/8.

Pot 4 : 33 4/8 : 27.

Pot 5 : 35 : 0.

Pot 5 : 38 : 18 3/8.

Pot 5 : 36 : 20 4/8.

Pot 5 : 37 4/8 : 34.

Pot 5 : 32 4/8 : 0.

Total : 399.38 : 199.00.

The twelve crossed plants now averaged 33.28, and the ten self-fertilised 19.9 inches in height, or as 100 to 60; so that they differed somewhat less than before.

The plants in Pots 3 and 5 were placed under a net in the greenhouse, two of the crossed plants in the latter pot being pulled up on account of the death of two of the self-fertilised; so that altogether six crossed and six self-fertilised plants were left to fertilise themselves spontaneously. The pots were rather small, and the plants did not produce many capsules. The small size of the self-fertilised plants will largely account for the fewness of the capsules which they produced. The six crossed plants bore 105, and the six self-fertilised only 30 capsules; or as 100 to 29.

The self-fertilised seeds thus obtained from the crossed and self-fertilised plants, after germinating on sand, were planted on the opposite sides of four small pots, and treated as before. But many of the plants were unhealthy, and their heights were so unequal--some on both sides being five times as tall as the others--that the averages deduced from the measurements in Table 5/73 are not in the least trustworthy. Nevertheless I have felt bound to give them, as they are opposed to my general conclusions.

The seven self-fertilised plants from the crossed plants here average 15.73, and the seven self-fertilised from the self-fertilised 21 inches in height; or as 100 to 133. Strictly a.n.a.logous experiments with Viola tricolor and Lathyrus odoratus gave a very different result.

TABLE 5/73. Nemophila insignis.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Self-fertilised Plants from Crossed Plants.

Column 3: Self-fertilised Plants from Self-fertilised Plants.

Pot 1 : 27 : 27 4/8.

Pot 1 : 14 : 34 2/8.

Pot 2 : 17 6/8 : 23.

Pot 2 : 24 4/8 : 32.

Pot 3 : 16 : 7.

Pot 4 : 5 3/8 : 7 2/8.

Pot 4 : 5 4/8 : 16.

Total : 110.13 : 147.00.

23. BORAGINACEAE.--Borago officinalis.

This plant is frequented by a greater number of bees than any other one which I have observed. It is strongly proterandrous (H. Muller 'Befruchtung' etc. page 267), and the flowers can hardly fail to be cross-fertilised; but should this not occur, they are capable of self-fertilisation to a limited extent, as some pollen long remains within the anthers, and is apt to fall on the mature stigma. In the year 1863 I covered up a plant, and examined thirty-five flowers, of which only twelve yielded any seeds; whereas of thirty-five flowers on an exposed plant growing close by, all with the exception of two yielded seeds. The covered-up plant, however, produced altogether twenty-five spontaneously self-fertilised seeds; the exposed plant producing fifty-five seeds, the product, no doubt, of cross-fertilisation.

In the year 1868 eighteen flowers on a protected plant were crossed with pollen from a distinct plant, but only seven of these produced fruit; and I suspect that I applied pollen to many of the stigmas before they were mature. These fruits contained on an average 2 seeds, with a maximum in one of three seeds. Twenty-four spontaneously self-fertilised fruits were produced by the same plant, and these contained on an average 1.2 seeds, with a maximum of two in one fruit. So that the fruits from the artificially crossed flowers yielded seeds compared with those from the spontaneously self-fertilised flowers, in the ratio of 100 to 60. But the self-fertilised seeds, as often occurs when few are produced, were heavier than the crossed seeds in the ratio of 100 to 90.