CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
TABLE 6/78. Petunia violacea (third generation; plants very young).
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 1 4/8 : 5 6/8. Pot 1 : 1 : 4 4/8.
Pot 2 : 5 7/8 : 8 3/8. Pot 2 : 5 6/8 : 6 7/8.
Pot 3 : 4 : 5 5/8.
Pot 4 : 1 4/8 : 5 3/8.
Total : 19.63 : 36.50.
The above seeds were placed on sand, and after germinating were planted in pairs on the opposite sides of four pots; and all the remaining seeds were thickly sown on the two sides of a fifth large pot. The result was surprising, for the self-fertilised seedlings very early in life beat the crossed, and at one time were nearly double their height. At first the case appeared like that of Mimulus, in which after the third generation a tall and highly self-fertile variety appeared. But as in the two succeeding generations the crossed plants resumed their former superiority over the self-fertilised, the case must be looked at as an anomaly. The sole conjecture which I can form is that the crossed seeds had not been sufficiently ripened, and thus produced weakly plants, as occurred with Iberis. When the crossed plants were between 3 and 4 inches in height, the six finest in four of the pots were measured to the summits of their stems, and at the same time the six finest of the self-fertilised plants. The measurements are given in Table 6/78, and it may be here seen that all the self-fertilised plants exceed their opponents in height, whereas when subsequently measured the excess of the self-fertilised depended chiefly on the unusual tallness of two of the plants in Pot 2. The crossed plants here average 3.27, and the self-fertilised 6.08 inches in height; or as 100 to 186.
When fully grown they were again measured, as follows:—
TABLE 6/79. Petunia violacea (third generation; plants fully grown).
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 41 4/8 : 40 6/8. Pot 1 : 48 : 39. Pot 1 : 36 : 48.
Pot 2 : 36 : 47. Pot 2 : 21 : 80 2/8. Pot 2 : 36 2/8 : 86 2/8.
Pot 3 : 52 : 46.
Pot 4 : 57 : 43 6/8.
Total : 327.75 : 431.00.
The eight crossed plants now averaged 40.96, and the eight self-fertilised plants 53.87 inches in height, or as 100 to 131; and this excess chiefly depended, as already stated, on the unusual tallness of two of the self-fertilised plants in Pot 2. The self-fertilised had therefore lost some of their former great superiority over the crossed plants. In three of the pots the self-fertilised plants flowered first; but in Pot 3 at the same time with the crossed.
The case is rendered the more strange, because the crossed plants in the fifth pot (not included in the two last tables), in which all the remaining seeds had been thickly sown, were from the first finer plants than the self-fertilised, and had larger leaves. At the period when the two tallest crossed plants in this pot were 6 4/8 and 4 5/8 inches high, the two tallest self-fertilised were only 4 inches. When the two crossed plants were 12 and 10 inches high, the two self-fertilised were only 8 inches. These latter plants, as well as many others on the same side of this pot never grew any higher, whereas several of the crossed plants grew to the height of two feet! On account of this great superiority of the crossed plants, the plants on neither side of this pot have been included in the two last tables.
Thirty flowers on the crossed plants in Pots 1 and 4 (Table 6/79) were again crossed, and produced seventeen capsules. Thirty flowers on the self-fertilised plants in the same two pots were again self-fertilised, but produced only seven capsules. The contents of each capsule of both lots were placed in separate watch-glasses, and the seeds from the crossed appeared to the eye to be at least double the number of those from the self-fertilised capsules.
In order to ascertain whether the fertility of the self-fertilised plants had been lessened by the plants having been self-fertilised for the three previous generations, thirty flowers on the crossed plants were fertilised with their own pollen. These yielded only five capsules, and their seeds being placed in separate watch-glasses did not seem more numerous than those from the capsules on the self-fertilised plants self-fertilised for the fourth time. So that as far as can be judged from so few capsules, the self-fertility of the self-fertilised plants had not decreased in comparison with that of the plants which had been intercrossed during the three previous generations. It should, however, be remembered that both lots of plants had been subjected in each generation to almost exactly similar conditions.
Seeds from the crossed plants again crossed, and from the self-fertilised again self-fertilised, produced by the plants in Pot 1 (Table 6/79), in which the three self-fertilised plants were on an average only a little taller than the crossed, were used in the following experiment. They were kept separate from two similar lots of seeds produced by the two plants in Pot 4 in the same table, in which the crossed plant was much taller than its self-fertilised opponent.
CROSSED AND SELF-FERTILISED PLANTS OF THE FOURTH GENERATION (RAISED FROM THE PLANTS IN POT 1, TABLE 6/79).
Crossed and self-fertilised seeds from plants of the last generation in Pot 1 in Table 6/79, were placed on sand, and after germinating, were planted in pairs on the opposite sides of four pots. The seedlings when in full flower were measured to the base of the calyx. The remaining seeds were sown crowded on the two sides of Pot 5; and the four tallest plants on each side of this pot were measured in the same manner.
TABLE 6/80. Petunia violacea (fourth generation; raised from plants of the third generation in Pot 1, table 6/79).
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 29 2/8 : 30 2/8. Pot 1 : 36 2/8 : 34 6/8. Pot 1 : 49 : 31 3/8.
Pot 2 : 33 3/8 : 31 5/8. Pot 2 : 37 3/8 : 38 2/8. Pot 2 : 56 4/8 : 38 4/8.
Pot 3 : 46 : 45 1/8. Pot 3 : 67 2/8 : 45. Pot 3 : 54 3/8 : 23 2/8.
Pot 4 : 51 6/8 : 34. Pot 4 : 51 7/8 : 0.
Pot 5 : 49 4/8 : 22 3/8. Pot 5 : 46 3/8 : 24 2/8. Pot 5 : 40 : 24 6/8. Pot 5 : 53 : 30. Crowded plants.
Total : 701.88 : 453.50.
The fifteen crossed plants average 46.79, and the fourteen (one having died) self-fertilised plants 32.39 inches in height; or as 100 to 69. So that the crossed plants in this generation had recovered their wonted superiority over the self-fertilised plants; though the parents of the latter in Pot 1, Table 6/79, were a little taller than their crossed opponents.
CROSSED AND SELF-FERTILISED PLANTS OF THE FOURTH GENERATION (RAISED FROM THE PLANTS IN POT 4, TABLE 6/79).
Two similar lots of seeds, obtained from the plants in Pot 4 in Table 6/79, in which the single crossed plant was at first shorter, but ultimately much taller than its self-fertilised opponent, were treated in every way like their brethren of the same generation in the last experiment. We have in Table 6/81 the measurements of the present plants. Although the crossed plants greatly exceeded in height the self-fertilised; yet in three out of the five pots a self-fertilised plant flowered before any one of the crossed; in a fourth pot simultaneously; and in a fifth (namely Pot 2) a crossed plant flowered first.
TABLE 6/81. Petunia violacea (fourth generation; raised from plants of the third generation in Pot 4, Table 6/79).
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 46 : 30 2/8. Pot 1 : 46 : 28.
Pot 2 : 50 6/8 : 25. Pot 2 : 40 2/8 : 31 3/8. Pot 2 : 37 3/8 : 22 4/8.
Pot 3 : 54 2/8 : 22 5/8. Pot 3 : 61 1/8 : 26 6/8. Pot 3 : 45 : 32.
Pot 4 : 30 : 24 4/8. Pot 4 : 29 1/8 : 26.
Pot 5 : 37 4/8 : 40 2/8. Pot 5 : 63 : 18 5/8. Pot 5 : 41 2/8 : 17 4/8. Crowded plants.
Total : 581.63 : 349.36.
The thirteen crossed plants here average 44.74, and the thirteen self-fertilised plants 26.87 inches in height; or as 100 to 60. The crossed parents of these were much taller, relatively to the self-fertilised parents, than in the last case; and apparently they transmitted some of this superiority to their crossed offspring. It is unfortunate that I did not turn these plants out of doors, so as to observe their relative fertility, for I compared the pollen from some of the crossed and self-fertilised plants in Pot 1, Table 6/81, and there was a marked difference in its state; that of the crossed plants contained hardly any bad and empty grains, whilst such abounded in the pollen of the self-fertilised plants.