Pot 9 : 49 : 30 3/8. Pot 9 : 50 3/8 : 15. Pot 9 : 46 3/8 : 36 7/8. Pot 9 : 47 6/8 : 44 1/8. Pot 9 : 0 : 31 6/8. Crowded Plants.
Pot 10 : 46 4/8 : 47 7/8. Pot 10 : 35 2/8 : 0. Pot 10 : 24 5/8 : 34 7/8. Pot 10 : 41 4/8 : 40 7/8. Pot 10 : 17 3/8 : 41 1/8. Crowded Plants.
Total : 1078.00 : 995.38.
The average height of the flower-stems on the twenty-five crossed plants in all the pots taken together is 43.12 inches, and that of the twenty-five self-fertilised plants 39.82, or as 100 to 92. In order to test this result, the plants planted in pairs in Pots 1 and 8 were considered by themselves, and the average height of the sixteen crossed plants is here 44.9, and that of the sixteen self-fertilised plants 42.03, or as 100 to 94. Again, the plants raised from the thickly sown seed in Pots 9 and 10, which were subjected to very severe mutual competition, were taken by themselves, and the average height of the nine crossed plants is 39.86, and that of the nine self-fertilised plants 35.88, or as 100 to 90. The plants in these two latter pots (9 and 10), after being measured, were cut down close to the ground and weighed: the nine crossed plants weighed 57.66 ounces, and the nine self-fertilised plants 45.25 ounces, or as 100 to 78. On the whole we may conclude, especially from the evidence of weight, that seedlings from a cross between flowers on the same plant have a decided, though not great, advantage over those from flowers fertilised with their own pollen, more especially in the case of the plants subjected to severe mutual competition. But the advantage is much less than that exhibited by the crossed offspring of distinct plants, for these exceeded the self-fertilised plants in height as 100 to 70, and in the number of flower-stems as 100 to 48. Digitalis thus differs from Ipomoea, and almost certainly from Mimulus, as with these two species a cross between flowers on the same plant did no good.
CALCEOLARIA.
A BUSHY GREENHOUSE VARIETY, WITH YELLOW FLOWERS BLOTCHED WITH PURPLE.
The flowers in this genus are constructed so as to favour or almost ensure cross-fertilisation (3/6. Hildebrand as quoted by H. Muller ‘Die Befruchtung der Blumen’ 1873 page 277.); and Mr. Anderson remarks that extreme care is necessary to exclude insects in order to preserve any kind true. (3/7. ‘Gardeners’ Chronicle’ 1853 page 534.) He adds the interesting statement, that when the corolla is cut quite away, insects, as far as he has seen, never discover or visit the flowers. This plant is, however, self-fertile if insects are excluded. So few experiments were made by me, that they are hardly worth giving. Crossed and self-fertilised seeds were sown on opposite sides of a pot, and after a time the crossed seedlings slightly exceeded the self-fertilised in height. When a little further grown, the longest leaves on the former were very nearly 3 inches in length, whilst those on the self-fertilised plants were only 2 inches. Owing to an accident, and to the pot being too small, only one plant on each side grew up and flowered; the crossed plant was 19 1/2 inches in height, and the self-fertilised one 15 inches; or as 100 to 77.
Linaria vulgaris.
It has been mentioned in the introductory chapter that two large beds of this plant were raised by me many years ago from crossed and self-fertilised seeds, and that there was a conspicuous difference in height and general appearance between the two lots. The trial was afterwards repeated with more care; but as this was one of the first plants experimented on, my usual method was not followed. Seeds were taken from wild plants growing in this neighbourhood and sown in poor soil in my garden. Five plants were covered with a net, the others being left exposed to the bees, which incessantly visit the flowers of this species, and which, according to H. Muller, are the exclusive fertilisers. This excellent observer remarks that, as the stigma lies between the anthers and is mature at the same time with them, self-fertilisation is possible. (3/8. ‘Die Befruchtung’ etc. page 279.) But so few seeds are produced by protected plants, that the pollen and stigma of the same flower seem to have little power of mutual interaction. The exposed plants bore numerous capsules forming solid spikes. Five of these capsules were examined and appeared to contain an equal number of seeds; and these being counted in one capsule, were found to be 166. The five protected plants produced altogether only twenty-five capsules, of which five were much finer than all the others, and these contained an average of 23.6 seeds, with a maximum in one capsule of fifty-five. So that the number of seeds in the capsules on the exposed plants to the average number in the finest capsules on the protected plants was as 100 to 14.
Some of the spontaneously self-fertilised seeds from under the net, and some seeds from the uncovered plants naturally fertilised and almost certainly intercrossed by the bees, were sown separately in two large pots of the same size; so that the two lots of seedlings were not subjected to any mutual competition. Three of the crossed plants when in full flower were measured, but no care was taken to select the tallest plants; their heights were 7 4/8, 7 2/8, and 6 4/8 inches; averaging 7.08 in height. The three tallest of all the self-fertilised plants were then carefully selected, and their heights were 6 3/8, 5 5/8, and 5 2/8, averaging 5.75 in height. So that the naturally crossed plants were to the spontaneously self-fertilised plants in height, at least as much as 100 to 81.