9. Petunia violacea.
The intercrossed plants of the same stock in four out of the five successive generations plainly exceeded in height the self-fertilised plants. The latter in the fourth generation were crossed by a fresh stock, and the seedlings thus obtained were put into competition with the self-fertilised plants of the fifth generation. The crossed plants exceeded the self-fertilised in height in the ratio of 100 to 66, and in weight as 100 to 23; but this difference, though so great, is not much greater than that between the intercrossed plants of the same stock in comparison with the self-fertilised plants of the corresponding generation. This case, therefore, seems at first sight opposed to the rule that a cross with a fresh stock is much more beneficial than a cross between individuals of the same stock. But as with Eschscholtzia, the reproductive system was here chiefly benefited; for the plants raised from the cross with the fresh stock were to the self-fertilised plants in fertility, both lots being naturally fertilised, as 100 to 46, whereas the intercrossed plants of the same stock were to the self-fertilised plants of the corresponding fifth generation in fertility only as 100 to 86.
Although at the time of measurement the plants raised from the cross with the fresh stock did not exceed in height or weight the intercrossed plants of the old stock (owing to the growth of the former not having been completed, as explained under the head of this species), yet they exceeded the intercrossed plants in fertility in the ratio of 100 to 54. This fact is interesting, as it shows that plants self-fertilised for four generations and then crossed by a fresh stock, yielded seedlings which were nearly twice as fertile as those from plants of the same stock which had been intercrossed for the five previous generations. We here see, as with Eschscholtzia and Dianthus, that the mere act of crossing, independently of the state of the crossed plants, has little efficacy in giving increased fertility to the offspring. The same conclusion holds good, as we have already seen, in the analogous cases of Ipomoea, Mimulus, and Dianthus, with respect to height.
10. Nicotiana tabacum.
My plants were remarkably self-fertile, and the capsules from the self-fertilised flowers apparently yielded more seeds than those which were cross-fertilised. No insects were seen to visit the flowers in the hothouse, and I suspect that the stock on which I experimented had been raised under glass, and had been self-fertilised during several previous generations; if so, we can understand why, in the course of three generations, the crossed seedlings of the same stock did not uniformly exceed in height the self-fertilised seedlings. But the case is complicated by individual plants having different constitutions, so that some of the crossed and self-fertilised seedlings raised at the same time from the same parents behaved differently. However this may be, plants raised from self-fertilised plants of the third generation crossed by a slightly different sub-variety, exceeded greatly in height and weight the self-fertilised plants of the fourth generation; and the trial was made on a large scale. They exceeded them in height when grown in pots, and not much crowded, in the ratio of 100 to 66; and when much crowded, as 100 to 54. These crossed plants, when thus subjected to severe competition, also exceeded the self-fertilised in weight in the ratio of 100 to 37. So it was, but in a less degree (as may be seen in Table 7/C), when the two lots were grown out of doors and not subjected to any mutual competition. Nevertheless, strange as is the fact, the flowers on the mother-plants of the third self-fertilised generation did not yield more seed when they were crossed with pollen from plants of the fresh stock than when they were self-fertilised.
11. Anagallis collina.
Plants raised from a red variety crossed by another plant of the same variety were in height to the self-fertilised plants from the red variety as 100 to 73. When the flowers on the red variety were fertilised with pollen from a closely similar blue-flowered variety, they yielded double the number of seeds to what they did when crossed by pollen from another individual of the same red variety, and the seeds were much finer. The plants raised from this cross between the two varieties were to the self-fertilised seedlings from the red variety, in height as 100 to 66, and in fertility as 100 to 6.
12. Primula veris.
Some flowers on long-styled plants of the third illegitimate generation were legitimately crossed with pollen from a fresh stock, and others were fertilised with their own pollen. From the seeds thus produced crossed plants, and self-fertilised plants of the fourth illegitimate generation, were raised. The former were to the latter in height as 100 to 46, and in fertility during one year as 100 to 5, and as 100 to 3.5 during the next year. In this case, however, we have no means of distinguishing between the evil effects of illegitimate fertilisation continued during four generations (that is, by pollen of the same form, but taken from a distinct plant) and strict self-fertilisation. But it is probable that these two processes do not differ so essentially as at first appears to be the case. In the following experiment any doubt arising from illegitimate fertilisation was completely eliminated.
13. Primula veris. (Equal-styled, red-flowered variety.)