The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 38

The seedlings thus raised may be called the Kew-crossed. Some other flowers on the same two plants were fertilised with their own pollen, and the seedlings thus raised from the fourth self-fertilised generation. The crossed capsules produced by the plant in Pot 2, Table 6/87, were plainly less fine than the self-fertilised capsules on the same plant. In Pot 5 the one finest capsule was also a self-fertilised one; but the seeds produced by the two crossed capsules together exceeded in number those produced by the two self-fertilised capsules on the same plant. Therefore as far as the flowers on the parent-plants are concerned, a cross with pollen from a fresh stock did little or no good; and I did not expect that the offspring would have received any benefit, but in this I was completely mistaken.

The crossed and self-fertilised seeds from the two plants were placed on bare sand, and very many of the crossed seeds of both sets germinated before the self-fertilised seeds, and protruded their radicles at a quicker rate. Hence many of the crossed seeds had to be rejected, before pairs in an equal state of germination were obtained for planting on the opposite sides of sixteen large pots. The two series of seedlings raised from the parent-plants in the two Pots 2 and 5 were kept separate, and when fully grown were measured to the tips of their highest leaves, as shown in Table 6/88. But as there was no uniform difference in height between the crossed and self-fertilised seedlings raised from the two plants, their heights have been added together in calculating the averages. I should state that by the accidental fall of a large bush in the greenhouse, several plants in both the series were much injured.

These were at once measured together with their opponents and afterwards thrown away. The others were left to grow to their full height, and were measured when in flower. This accident accounts for the small height of some of the pairs; but as all the pairs, whether only partly or fully grown, were measured at the same time, the measurements are fair.

The average height of the twenty-six crossed plants in the sixteen pots of the two series is 63.29, and that of the twenty-six self-fertilised plants is 41.67 inches; or as 100 to 66. The superiority of the crossed plants was shown in another way, for in every one of the sixteen pots a crossed plant flowered before a self-fertilised one, with the exception of Pot 6 of the second series, in which the plants on the two sides flowered simultaneously.

TABLE 6/88. Nicotiana tabac.u.m. Plants raised from two plants of the third self-fertilised generation in Pots 2 and 5, in Table 6/87.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Kew-crossed Plants, pot 2, Table 6/87.

Column 3: Plants of the fourth Self-fertilised generation, pot 2, Table 6/87.

Column 4: Kew-crossed Plants, pot 5, Table 6/87.

Column 5: Plants of the fourth Self-fertilised generation, pot 5, Table 6/87.

Pot 1 : 84 6/8 : 68 4/8 : 77 6/8 : 56.

Pot 1 : 31 : 5 : 7 2/8 : 5 3/8.

Pot 2 : 78 4/8 : 51 4/8 : 55 4/8 : 27 6/8.

Pot 2 : 48 : 70 : 18 : 7.

Pot 3 : 77 3/8 : 12 6/8 : 76 2/8 : 60 6/8.

Pot 3 : 77 1/8 : 6 6/8.

Pot 4 : 49 2/8 : 29 4/8 : 90 4/8 : 11 6/8.

Pot 4 : 15 6/8 : 32 : 22 2/8 : 4 1/8.

Pot 5 : 89 : 85 : 94 2/8 : 28 4/8.

Pot 5 : 17 : 5 3/8.

Pot 6 : 90 : 80 : 78 : 78 6/8.

Pot 7 : 84 4/8 : 48 6/8 : 85 4/8 : 61 4/8.

Pot 7 : 76 4/8 : 56 4/8.

Pot 8 : 83 4/8 : 84 4/8 : 65 5/8 : 78 3/8.

Pot 8 : : : 72 2/8 : 27 4/8.

Total : 902.63 : 636.13 : 743.13 : 447.38.

Some of the remaining seeds of both series, whether or not in a state of germination, were thickly sown on the opposite sides of two very large pots; and the six highest plants on each side of each pot were measured after they had grown to nearly their full height. But their heights were much less than in the former trials, owing to their extremely crowded condition. Even whilst quite young, the crossed seedlings manifestly had much broader and finer leaves than the self-fertilised seedlings.

TABLE 6/89. Nicotiana tabac.u.m. Plants of the same parentage as those in Table 6/88, but grown extremely crowded in two large pots.

Heights of plants measured in inches.

Column 1: Kew-crossed Plants, from pot 2, Table 6/87.

Column 2: Plants of the fourth Self-fertilised generation, from pot 2, Table 6/87.

Column 3: Kew-crossed Plants, from pot 5, Table 6/87.

Column 4: Plants of the fourth Self-fertilised generation, from pot 5, Table 6/87.

42 4/8 : 22 4/8 : 44 6/8 : 22 4/8.

34 : 19 2/8 : 42 4/8 : 21.

30 4/8 : 14 2/8 : 27 4/8 : 18.

23 4/8 : 16 : 31 2/8 : 15 2/8.

26 6/8 : 13 4/8 : 32 : 13 5/8.

18 3/8 : 16 : 24 6/8 : 14 6/8.

175.63 : 101.50 : 202.75 : 105.13.

The twelve tallest crossed plants in the two pots belonging to the two series average here 31.53, and the twelve tallest self-fertilised plants 17.21 inches in height; or as 100 to 54. The plants on both sides, when fully grown, some time after they had been measured, were cut down close to the ground and weighed. The twelve crossed plants weighed 21.25 ounces; and the twelve self-fertilised plants only 7.83 ounces; or in weight as 100 to 37.

The rest of the crossed and self-fertilised seeds from the two parent-plants (the same as in the last experiment) was sown on the 1st of July in four long parallel and separate rows in good soil in the open ground; so that the seedlings were not subjected to any mutual compet.i.tion. The summer was wet and unfavourable for their growth.

Whilst the seedlings were very small the two crossed rows had a clear advantage over the two self-fertilised rows. When fully grown the twenty tallest crossed plants and the twenty tallest self-fertilised plants were selected and measured on the 11th of November to the extremities of their leaves, as shown in Table 6/90. Of the twenty crossed plants, twelve had flowered; whilst of the twenty self-fertilised plants one alone had flowered.

TABLE 6/90. Nicotiana tabac.u.m. Plants raised from the same seeds as in the last two experiments, but sown separately in the open ground, so as not to compete together.

Heights of plants measured in inches.

Column 1: Kew-crossed Plants, from pot 2, Table 6/87.

Column 2: Plants of the fourth Self-fertilised generation, from pot 2, Table 6/87.

Column 3: Kew-crossed Plants, from pot 5, Table 6/87.

Column 4: Plants of the fourth Self-fertilised generation, from pot 5, Table 6/87.

42 2/8 : 22 6/8 : 54 4/8 : 34 4/8.

54 5/8 : 37 4/8 : 51 4/8 : 38 5/8.

39 3/8 : 34 4/8 : 45 : 40 6/8.

53 2/8 : 30 : 43 : 43 2/8.

49 3/8 : 28 6/8 : 43 : 40.

50 3/8 : 31 2/8 : 48 6/8 : 38 2/8.

47 1/8 : 25 4/8 : 44 : 35 6/8.

57 3/8 : 26 2/8 : 48 2/8 : 39 6/8.

37 : 22 3/8 : 55 1/8 : 47 6/8.

48 : 28 : 63 : 58 5/8.

478.75 : 286.86 : 496.13 : 417.25

The twenty tallest crossed plants here average 48.74, and the twenty tallest self-fertilised 35.2 inches in height; or as 100 to 72. These plants after being measured were cut down close to the ground, and the twenty crossed plants weighed 195.75 ounces, and the twenty self-fertilised plants 123.25 ounces; or as 100 to 63.