The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom Part 22

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 28 6/8 : 30.

Pot 1 : 27 3/8 : 26.

Pot 2 : 29 : 30 7/8.

Pot 2 : 29 4/8 : 27 4/8.

Pot 3 : 28 4/8 : 31 6/8.

Pot 3 : 23 4/8 : 24 5/8.

Pot 4 : 27 : 30.

Pot 4 : 33 4/8 : 25.

Total : 227.13 : 225.75.

The average height of the eight crossed plants is here 28.39 inches, and of the eight self-fertilised 28.21; or as 100 to 99. So that there was no difference in height worth speaking of; but in general vigour and luxuriance there was an astonis.h.i.+ng difference, as shown by their weights. After the seed-capsules had been gathered, the eight crossed and the eight self-fertilised plants were cut down and weighed; the former weighed 43 ounces, and the latter only 21 ounces; or as 100 to 49.

These plants were all kept under a net, so that the capsules which they produced must have been all spontaneously self-fertilised. The eight crossed plants produced twenty-one such capsules, of which only twelve contained any seed, averaging 8.5 per capsule. On the other hand, the eight self-fertilised plants produced no less than thirty-six capsules, of which I examined twenty-five, and, with the exception of three, all contained seeds, averaging 10.63 seeds per capsule. Thus the proportional number of seeds per capsule produced by the plants of crossed origin to those produced by the plants of self-fertilised origin (both lots being spontaneously self-fertilised) was as 100 to 125. This anomalous result is probably due to some of the self-fertilised plants having varied so as to mature their pollen and stigmas more nearly at the same time than is proper to the species; and we have already seen that some plants in the first experiment differed from the others in being slightly more self-fertile.

THE EFFECTS OF A CROSS WITH A FRESH STOCK.

Twenty flowers on the self-fertilised plants of the last or third generation, in Table 4/46, were fertilised with their own pollen, but taken from other flowers on the same plants. These produced fifteen capsules, which contained (omitting two with only three and six seeds) on an average 47.23 seeds, with a maximum of seventy in one. The self-fertilised capsules from the self-fertilised plants of the first generation yielded the much lower average of 35.95 seeds; but as these latter plants grew extremely crowded, nothing can be inferred with respect to this difference in their self-fertility. The seedlings raised from the above seeds const.i.tute the plants of the fourth self-fertilised generation in Table 4/47.

Twelve flowers on the same plants of the third self-fertilised generation, in Table 4/46, were crossed with pollen from the crossed plants in the same table. These crossed plants had been intercrossed for the three previous generations; and many of them, no doubt, were more or less closely inter-related, but not so closely as in some of the experiments with other species; for several carnation plants had been raised and crossed in the earlier generations. They were not related, or only in a distant degree, to the self-fertilised plants. The parents of both the self-fertilised and crossed plants had been subjected to as nearly as possible the same conditions during the three previous generations. The above twelve flowers produced ten capsules, containing on an average 48.66 seeds, with a maximum in one of seventy-two seeds.

The plants raised from these seeds may be called the INTERCROSSED.

Lastly, twelve flowers on the same self-fertilised plants of the third generation were crossed with pollen from plants which had been raised from seeds purchased in London. It is almost certain that the plants which produced these seeds had grown under very different conditions to those to which my self-fertilised and crossed plants had been subjected; and they were in no degree related. The above twelve flowers thus crossed all produced capsules, but these contained the low average of 37.41 seeds per capsule, with a maximum in one of sixty-four seeds. It is surprising that this cross with a fresh stock did not give a much higher average number of seeds; for, as we shall immediately see, the plants raised from these seeds, which may be called the LONDON-CROSSED, benefited greatly by the cross, both in growth and fertility.

The above three lots of seeds were allowed to germinate on bare sand.

Many of the London-crossed germinated before the others, and were rejected; and many of the intercrossed later than those of the other two lots. The seeds after thus germinating were planted in ten pots, made tripart.i.te by superficial divisions; but when only two kinds of seeds germinated at the same time, they were planted on the opposite sides of other pots; and this is indicated by blank s.p.a.ces in one of the three columns in Table 4/47. A 0 in the table signifies that the seedling died before it was measured; and a + signifies that the plant did not produce a flower-stem, and therefore was not measured. It deserves notice that no less than eight out of the eighteen self-fertilised plants either died or did not flower; whereas only three out of the eighteen intercrossed, and four out of the twenty London-crossed plants, were in this predicament. The self-fertilised plants had a decidedly less vigorous appearance than the plants of the other two lots, their leaves being smaller and narrower. In only one pot did a self-fertilised plant flower before one of the two kinds of crossed plants, between which there was no marked difference in the period of flowering. The plants were measured to the base of the calyx, after they had completed their growth, late in the autumn.

TABLE 4/47. Dianthus caryophyllus.

Heights of plants to the base of the calyx, measured in inches.

Column 1: Number (Name) of Pot.

Column 2: London-Crossed Plants.

Column 3: Intercrossed Plants.

Column 4: Self-fertilised Plants.

Pot 1 : 39 5/8 : 25 1/8 : 29 2/8.

Pot 1 : 30 7/8 : 21 6/8 : +.

Pot 2 : 36 2/8 : : 22 3/8.

Pot 2 : 0 : : +.

Pot 3 : 28 5/8 : 30 2/8 : .

Pot 3 : + : 23 1/8 : .

Pot 4 : 33 4/8 : 35 5/8 : 30.

Pot 4 : 28 7/8 : 32 : 24 4/8.

Pot 5 : 28 : 34 4/8 : +.

Pot 5 : 0 : 24 2/8 : +.

Pot 6 : 32 5/8 : 24 7/8 : 30 3/8.

Pot 6 : 31 : 26 : 24 4/8.

Pot 7 : 41 7/8 : 29 7/8 : 27 7/8.

Pot 7 : 34 7/8 : 26 4/8 : 27.

Pot 8 : 34 5/8 : 29 : 26 6/8.

Pot 8 : 28 5/8 : 0 : +.

Pot 9 : 25 5/8 : 28 5/8 : +.

Pot 9 : 0 : + : 0.

Pot 10 : 38 : 28 4/8 : 22 7/8.

Pot 10 : 32 1/8 : + : 0.

Total : 525.13 : 420.00 : 265.50.

The average height of the sixteen London-crossed plants in Table 4/47 is 32.82 inches; that of the fifteen intercrossed plants, 28 inches; and that of the ten self-fertilised plants, 26.55.

So that in height we have the following ratios:--

The London-crossed to the self-fertilised as 100 to 81.

The London-crossed to the intercrossed as 100 to 85.

The intercrossed to the self-fertilised as 100 to 95.

These three lots of plants, which it should be remembered were all derived on the mother-side from plants of the third self-fertilised generation, fertilised in three different ways, were left exposed to the visits of insects, and their flowers were freely crossed by them. As the capsules of each lot became ripe they were gathered and kept separate, the empty or bad ones being thrown away. But towards the middle of October, when the capsules could no longer ripen, all were gathered and were counted, whether good or bad. The capsules were then crushed, and the seed cleaned by sieves and weighed. For the sake of uniformity the results are given from calculation, as if there had been twenty plants in each lot.

The sixteen London-crossed plants actually produced 286 capsules; therefore twenty such plants would have produced 357.5 capsules; and from the actual weight of the seeds, the twenty plants would have yielded 462 grains weight of seeds.

The fifteen intercrossed plants actually produced 157 capsules; therefore twenty of them would have produced 209.3 capsules and the seeds would have weighed 208.48 grains.

The ten self-fertilised plants actually produced 70 capsules, therefore twenty of them would have produced 140 capsules; and the seeds would have weighed 153.2 grains.

From these data we get the following ratios:--

NUMBER OF CAPSULES PRODUCED BY AN EQUAL NUMBER OF PLANTS OF THE THREE LOTS.