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Show 266 SUMMARY OF MEASUREMENTS. CHAP. VII. intercrossed plants of the same stock were to the selffertilised plants of the corresponding fifth generation in fertility only as 100 to 86. Although at the time of measurement tho plants raised from the cross with th fresh stoek did not exceed in height or weight the intorcrossed plants of the old stock (owing to the growth of tho 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 f~r 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 E chscholtzia and Dianthus that the mere act of crossing, independently of the sta' te of the cro~s~d plants, has little efficacy in giving increased fertihty to the offspring. The same conclusion holds good, as we have already seen, in the analogous cases of Ipomcea, Mimulus, and Dianthus, with respect to height. (10.) Nicotiana tabacum.-My plants were remarkably self-fertile, and the capsules fro1n the self-fertilised flowers apparently yielded more s eels than those which were cross-fertilised. No insects wore 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, w can under. tand why, in the course of three generations, the crossed seedlings of the same s~ock did I~ot uniformly exceed in height the self-~ert~h. se~ seedhngs. But the case is complicated by IndiVIdual plants having different constitutions, so that some of the crossed and self-fertilised se0dlings raised at the same ti1ne fro1n the same parents behaved differently. CHAP. VII. TABLE C. 267 However this 1nay 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 0), 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 1nore seed when they were crossed with pollen from plants of the fresh stock than when they were self-fertilised. (11.) A nag allis 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, arid the seeds were much :finer. The plants raised from this cross between the two varieties wer~ to the self-fertilised seedlings from the red variety, in height as 100 to 66, and in fertility ·as 100 to 6. (12.) Pri1nula 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. Frmn the seeds thus produced crossed plants, and self- |
