The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 16

Pot 4 : 17 1/8 : 16 4/8.

Pot 4 : 18 7/8 : 14 4/8.

Pot 4 : 17 5/8 : 16.

Pot 4 : 15 6/8 : 15 3/8.

Pot 4 : 14 4/8 : 14 7/8.

Pot 5 : 18 1/8 : 16 4/8.

Pot 5 : 14 7/8 : 16 2/8.

Pot 5 : 16 2/8 : 14 2/8.

Pot 5 : 15 5/8 : 14 2/8.

Pot 5 : 12 4/8 : 16 1/8.

Pot 6 : 18 6/8 : 16 1/8.

Pot 6 : 18 6/8 : 15.

Pot 6 : 17 3/8 : 15 2/8.

Pot 7 : 18 : 16 3/8.

Pot 7 : 16 4/8 : 14 4/8.

Pot 7 : 18 2/8 : 13 5/8.

Pot 8 : 20 6/8 : 15 6/8.

Pot 8 : 17 7/8 : 16 3/8.

Pot 8 : 13 5/8 : 20 2/8.

Pot 8 : 19 2/8 : 15 6/8.

Total : 520.38 : 449.88.

The average height of the thirty crossed plants is here 17.34, and that of the twenty-nine self-fertilised plants (one having died) 15.51, or as 100 to 89. I am surprised that the difference did not prove somewhat greater, considering that in the last experiment it was as 100 to 86; but this latter ratio, as before explained, was probably too great. It should, however, be observed that in the last experiment (Table 4/31), the crossed plants competed with plants of the third self-fertilised generation; whilst in the present case, plants derived from a cross with a fresh stock competed with self-fertilised plants of the first generation.

The crossed plants in the present case, as in the last, were more fertile than the self-fertilised, both lots being left uncovered in the greenhouse. The thirty crossed plants produced 103 seed-bearing flowers-heads, as well as some heads which yielded no seeds; whereas the twenty-nine self-fertilised plants produced only 81 seed-bearing heads; therefore thirty such plants would have produced 83.7 heads. We thus get the ratio of 100 to 81, for the number of seed-bearing flower-heads produced by the crossed and self-fertilised plants. Moreover, a number of seed-bearing heads from the crossed plants, compared with the same number from the self-fertilised, yielded seeds by weight, in the ratio of 100 to 92. Combining these two elements, namely, the number of seed-bearing heads and the weight of seeds in each head, the productiveness of the crossed to the self-fertilised plants was as 100 to 75.

The crossed and self-fertilised seeds, which remained after the above pairs had been planted, (some in a state of germination and some not so), were sown early in the year out of doors in two rows. Many of the self-fertilised seedlings suffered greatly, and a much larger number of them perished than of the crossed. In the autumn the surviving self-fertilised plants were plainly less well-grown than the crossed plants.

7. PAPAVERACEAE.--Papaver vagum.

A SUB-SPECIES OF Papaver dubium, FROM THE SOUTH OF FRANCE.

The poppy does not secrete nectar, but the flowers are highly conspicuous and are visited by many pollen-collecting bees, flies and beetles. The anthers shed their pollen very early, and in the case of Papaver rhoeas, it falls on the circ.u.mference of the radiating stigmas, so that this species must often be self-fertilised; but with Papaver dubium the same result does not follow (according to H. Muller 'Die Befruchtung' page 128), owing to the shortness of the stamens, unless the flower happens to stand inclined. The present species, therefore, does not seem so well fitted for self-fertilisation as most of the others. Nevertheless Papaver vagum produced plenty of capsules in my garden when insects were excluded, but only late in the season. I may here add that Papaver somniferum produces an abundance of spontaneously self-fertilised capsules, as Professor H. Hoffmann likewise found to be the case. (4/2. 'Zur Speciesfrage' 1875 page 53.) Some species of Papaver cross freely when growing in the same garden, as I have known to be the case with Papaver bracteatum and orientale.

Plants of Papaver vagum were raised from seeds sent me from Antibes through the kindness of Dr. Bornet. Some little time after the flowers had expanded, several were fertilised with their own pollen, and others (not castrated) with pollen from a distinct individual; but I have reason to believe, from observations subsequently made, that these flowers had been already fertilised by their own pollen, as this process seems to take place soon after their expansion. (4/3. Mr. J. Scott found 'Report on the Experimental Culture of the Opium Poppy' Calcutta 1874 page 47, in the case of Papaver somniferum, that if he cut away the stigmatic surface before the flower had expanded, no seeds were produced; but if this was done "on the second day, or even a few hours after the expansion of the flower on the first day, a partial fertilisation had already been effected, and a few good seeds were almost invariably produced." This proves at how early a period fertilisation takes place.) I raised, however, a few seedlings of both lots, and the self-fertilised rather exceeded the crossed plants in height.

Early in the following year I acted differently, and fertilised seven flowers, very soon after their expansion, with pollen from another plant, and obtained six capsules. From counting the seeds in a medium-sized one, I estimated that the average number in each was at least 120. Four out of twelve capsules, spontaneously self-fertilised at the same time, were found to contain no good seeds; and the remaining eight contained on an average 6.6 seeds per capsule. But it should be observed that later in the season the same plants produced under a net plenty of very fine spontaneously self-fertilised capsules.

The above two lots of seeds, after germinating on sand, were planted in pairs on opposite sides of five pots. The two lots of seedlings, when half an inch in height, and again when 6 inches high, were measured to the tips of their leaves, but presented no difference. When fully grown, the flower-stalks were measured to the summits of the seed capsules, with the following result:--

TABLE 4/33. Papaver vagum.

Heights of flower-stalks to the summits of the seed capsules measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 24 2/8 : 21.

Pot 1 : 30 : 26 5/8.

Pot 1 : 18 4/8 : 16.

Pot 2 : 14 4/8 : 15 3/8.

Pot 2 : 22 : 20 1/8.

Pot 2 : 19 5/8 : 14 1/8.

Pot 2 : 21 5/8 : 16 4/8.

Pot 3 : 20 6/8 : 19 2/8.

Pot 3 : 20 2/8 : 13 2/8.

Pot 3 : 20 6/8 : 18.

Pot 4 : 25 3/8 : 23 2/8.

Pot 4 : 24 2/8 : 23.

Pot 5 : 20 : 18 3/8.

Pot 5 : 27 7/8 : 27.

Pot 5 : 19 : 21 2/8.

Total : 328.75 : 293.13.

The fifteen crossed plants here average 21.91 inches, and the fifteen self-fertilised plants 19.54 inches in height, or as 100 to 89. These plants did not differ in fertility, as far as could be judged by the number of capsules produced, for there were seventy-five on the crossed side and seventy-four on the self-fertilised side.

Eschscholtzia californica.

This plant is remarkable from the crossed seedlings not exceeding in height or vigour the self-fertilised. On the other hand, a cross greatly increases the productiveness of the flowers on the parent-plant, and is indeed sometimes necessary in order that they should produce any seed; moreover, plants thus derived are themselves much more fertile than those raised from self-fertilised flowers; so that the whole advantage of a cross is confined to the reproductive system. It will be necessary for me to give this singular case in considerable detail.

Twelve flowers on some plants in my flower-garden were fertilised with pollen from distinct plants, and produced twelve capsules; but one of these contained no good seed. The seeds of the eleven good capsules weighed 17.4 grains. Eighteen flowers on the same plants were fertilised with their own pollen and produced twelve good capsules, which contained 13.61 grains weight of seed. Therefore an equal number of crossed and self-fertilised capsules would have yielded seed by weight as 100 to 71.

(4/4. Professor Hildebrand experimented on plants in Germany on a larger scale than I did, and found them much more self-fertile. Eighteen capsules, produced by cross-fertilisation, contained on an average eighty-five seeds, whilst fourteen capsules from self-fertilised flowers contained on an average only nine seeds; that is, as 100 to 11: 'Jahrb.

fur Wissen Botanik.' B. 7 page 467.) If we take into account of the fact that a much greater proportion of flowers produced capsules when crossed than when self-fertilised, the relative fertility of the crossed to the self-fertilised flowers was as 100 to 52. Nevertheless these plants, whilst still protected by the net, spontaneously produced a considerable number of self-fertilised capsules.

The seeds of the two lots after germinating on sand were planted in pairs on the opposite sides of four large pots. At first there was no difference in their growth, but ultimately the crossed seedlings exceeded the self-fertilised considerably in height, as shown in Table 4/34. But I believe from the cases which follow that this result was accidental, owing to only a few plants having been measured, and to one of the self-fertilised plants having grown only to a height of 15 inches. The plants had been kept in the greenhouse, and from being drawn up to the light had to be tied to sticks in this and the following trials. They were measured to the summits of their flower-stems.

TABLE 4/34. Eschscholtzia californica.

Heights of Plants to the summits of their flower-stems measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.