Twelve flowers on some plants of the common tobacco, raised from purchased seeds, were crossed with pollen from a distinct plant of the same lot, and these produced ten capsules. Twelve flowers on the same plants were fertilised with their own pollen, and produced eleven capsules. The seeds in the ten crossed capsules weighed 31.7 grains, whilst those in ten of the self-fertilised capsules weighed 47.67 grains; or as 100 to 150. The much greater productiveness of the self-fertilised than of the crossed capsules can hardly be attributed to chance, as all the capsules of both lots were very fine and healthy ones.
The seeds were placed on sand, and several pairs in an equal state of germination were planted on the opposite sides of three pots. The remaining seeds were thickly sown on the two sides of Pot 4, so that the plants in this pot were much crowded. The tallest plant on each side of each pot was measured. Whilst the plants were quite young the four tallest crossed plants averaged 7.87 inches, and the four tallest self-fertilised 14.87 inches in height; or as 100 to 189. The heights at this age are given in the two left columns of Table 6/84.
When in full flower the tallest plants on each side were again measured, see the two right hand columns in Table 6/84. But I should state that the pots were not large enough, and the plants never grew to their proper height. The four tallest crossed plants now averaged 18.5, and the four tallest self-fertilised plants 32.75 inches in height; or as 100 to 178. In all four pots a self-fertilised plant flowered before any one of the crossed.
In Pot 4, in which the plants were extremely crowded, the two lots were at first equal; and ultimately the tallest crossed plant exceeded by a trifle the tallest self-fertilised plant. This recalled to my mind an analogous case in the one generation of Petunia, in which the self-fertilised plants were throughout their growth taller than the crossed in all the pots except in the crowded one. Accordingly another trial was made, and some of the same crossed and self-fertilised seeds of tobacco were sown thickly on opposite sides of two additional pots; the plants being left to grow up much crowded. When they were between 13 and 14 inches in height there was no difference between the two sides, nor was there any marked difference when the plants had grown as tall as they could; for in one pot the tallest crossed plant was 26 1/2 inches in height, and exceeded by 2 inches the tallest self-fertilised plant, whilst in the other pot, the tallest crossed plant was shorter by 3 1/2 inches than the tallest self-fertilised plant, which was 22 inches in height.
TABLE 6/84. Nicotiana tabacum (first generation).
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants, May 20, 1868.
Column 3: self-fertilised Plants, May 20, 1868.
Column 4: Crossed Plants, December 6, 1868.