The same plants were again measured in the autumn of the following year, 1870.
TABLE 5/60. Pot 2.—Sarothamnus scoparius.
Heights of plants measured in inches.
Column 1: Crossed Plants.
Column 2: Self-fertilised Plants.
Total : 56.75 : 35.50.
The three crossed plants now averaged 18.91, and the three self-fertilised 11.83 inches in height; or as 100 to 63. The three crossed plants in Pot 1, as already shown, had beaten the three self-fertilised plants so completely, that any comparison between them was superfluous.
The winter of 1870-1871 was severe. In the spring the three crossed plants in Pot 2 had not even the tips of their shoots in the least injured, whereas all three self-fertilised plants were killed half-way down to the ground; and this shows how much more tender they were. In consequence not one of these latter plants bore a single flower during the ensuing summer of 1871, whilst all three crossed plants flowered.
Ononis minutissima.
This plant, of which seeds were sent me from North Italy, produces, besides the ordinary papilionaceous flowers, minute, imperfect, closed or cleistogene flowers, which can never be cross-fertilised, but are highly self-fertile. Some of the perfect flowers were crossed with pollen from a distinct plant, and six capsules thus produced yielded on an average 3.66 seeds, with a maximum of five in one. Twelve perfect flowers were marked and allowed to fertilise themselves spontaneously under a net, and they yielded eight capsules, containing on an average 2.38 seeds, with a maximum of three seeds in one. So that the crossed and self-fertilised capsules from the perfect flowers yielded seeds in the proportion of 100 to 65. Fifty-three capsules produced by the cleistogene flowers contained on an average 4.1 seeds, so that these were the most productive of all; and the seeds themselves looked finer even than those from the crossed perfect flowers.
The seeds from the crossed perfect flowers and from the self-fertilised cleistogene flowers were allowed to germinate on sand; but unfortunately only two pairs germinated at the same time. These were planted on the opposite sides of the same pot, which was kept in the greenhouse. In the summer of the same year, when the seedlings were about 4 1/2 inches in height, the two lots were equal. In the autumn of the following year (1868) the two crossed plants were of exactly the same height, namely, 11 4/8 inches, and the two self-fertilised plants 12 6/8 and 7 2/8 inches; so that one of the self-fertilised exceeded considerably in height all the others. By the autumn of 1869 the two crossed plants had acquired the supremacy; their height being 16 4/8 and 15 1/8, whilst that of the two self-fertilised plants was 14 5/8 and 11 4/8 inches.
By the autumn of 1870, the heights were as follows:—
TABLE 5/61. Ononis minutissima.
Heights of plants measured in inches.
Column 1: Crossed Plants.
Column 2: Self-fertilised Plants.
Total : 39.63 : 34.75.
So that the mean height of the two crossed plants was 19.81, and that of the two self-fertilised 17.37 inches; or as 100 to 88. It should be remembered that the two lots were at first equal in height; that one of the self-fertilised plants then had the advantage, the two crossed plants being at last victorious.]
Six genera in this family were experimented on, and the results are in some respects remarkable. The crossed plants of the two species of Lupinus were conspicuously superior to the self-fertilised plants in height and fertility; and when grown under very unfavourable conditions, in vigour. The scarlet-runner (Phaseolus multiflorus) is partially sterile if the visits of bees are prevented, and there is reason to believe that varieties growing near one another intercross. The five crossed plants, however, exceeded in height the five self-fertilised only by a little. Phaseolus vulgaris is perfectly self-sterile; nevertheless, varieties growing in the same garden sometimes intercross largely. The varieties of Lathyrus odoratus, on the other hand, appear never to intercross in this country; and though the flowers are not often visited by efficient insects, I cannot account for this fact, more especially as the varieties are believed to intercross in North Italy. Plants raised from a cross between two varieties, differing only in the colour of their flowers, grew much taller and were under unfavourable conditions more vigorous than the self-fertilised plants; they also transmitted, when self-fertilised, their superiority to their offspring. The many varieties of the common Pea (Pisum sativum), though growing in close proximity, very seldom intercross; and this seems due to the rarity in this country of the visits of bees sufficiently powerful to effect cross-fertilisation. A cross between the self-fertilised individuals of the same variety does no good whatever to the offspring; whilst a cross between distinct varieties, though closely allied, does great good, of which we have excellent evidence. The flowers of the Broom (Sarothamnus) are almost sterile if they are not disturbed and if insects are excluded. The pollen from a distinct plant is more effective than that from the same flower in producing seeds. The crossed seedlings have an enormous advantage over the self-fertilised when grown together in close competition. Lastly, only four plants of the Ononis minutissima were raised; but as these were observed during their whole growth, the advantage of the crossed over the self-fertilised plants may, I think, be fully trusted.
[15. ONAGRACEAE.—Clarkia elegans.
Owing to the season being very unfavourable (1867), few of the flowers which I fertilised formed capsules; twelve crossed flowers produced only four, and eighteen self-fertilised flowers yielded only one capsule. The seeds after germinating on sand were planted in three pots, but all the self-fertilised plants died in one of them. When the two lots were between 4 and 5 inches in height, the crossed began to show a slight superiority over the self-fertilised. When in full flower they were measured, with the following result:—
TABLE 5/62. Clarkia elegans.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 40 4/8 : 33. Pot 1 : 35 : 24. Pot 1 : 25 : 23.
Pot 2 : 33 4/8 : 30 4/8.
Total : 134.0 : 110.5.
The average height of the four crossed plants is 33.5, and that of the four self-fertilised plants 27.62 inches, or as 100 to 82. The crossed plants altogether produced 105 and the self-fertilised plants 63 capsules; or as 100 to 60. In both pots a self-fertilised plant flowered before any one of the crossed plants.
16. LOASACEAE.—Bartonia aurea.
Some flowers were crossed and self-fertilised in the usual manner during two seasons; but as I reared on the first occasion only two pairs, the results are given together. On both occasions the crossed capsules contained slightly more seeds than the self-fertilised. During the first year, when the plants were about 7 inches in height, the self-fertilised were the tallest, and in the second year the crossed were the tallest. When the two lots were in full flower they were measured, as in Table 5/63.
TABLE 5/63. Bartonia aurea.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 31 : 37.
Pot 2 : 18 4/8 : 20 4/8.
Pot 3 : 19 4/8 : 40 4/8.
Pot 4 : 25 : 35. Pot 4 : 36 : 15 4/8.
Pot 5 : 31 : 18. Pot 5 : 16 : 11 4/8.
Pot 6 : 20 : 32 4/8.
Total : 197.0 : 210.5.
The average height of the eight crossed plants is 24.62, and that of the eight self-fertilised 26.31 inches; or as 100 to 107. So that the self-fertilised had a decided advantage over the crossed. But the plants from some cause never grew well, and finally became so unhealthy that only three crossed and three self-fertilised plants survived to set any capsules, and these were few in number. The two lots seemed to be about equally unproductive.
17. PASSIFLORACEAE.—Passiflora gracilis.
This annual species produces spontaneously numerous fruits when insects are excluded, and behaves in this respect very differently from most of the other species in the genus, which are extremely sterile unless fertilised with pollen from a distinct plant. (5/17. ‘Variation of Animals and Plants under Domestication’ chapter 17 2nd edition volume 2 page 118.) Fourteen fruits from crossed flowers contained on an average 24.14 seeds. Fourteen fruits (two poor ones being rejected), spontaneously self-fertilised under a net, contained on an average 20.58 seeds per fruit; or as 100 to 85. These seeds were sown on the opposite sides of three pots, but only two pairs came up at the same time; and therefore a fair judgment cannot be formed.
TABLE 5/64. Passiflora gracilis.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 56 : 38.
Pot 2 : 42 : 64.
Total : 98 : 102.
The mean of the two crossed is 49 inches, and that of the two self-fertilised 51 inches; or as 100 to 104.
18. UMBELLIFERAE.—Apium petroselinum.
The Umbelliferae are proterandrous, and can hardly fail to be cross-fertilised by the many flies and small Hymenoptera which visit the flowers. (5/18. Hermann Muller ‘Befruchtung’ etc. page 96. According to M. Mustel as stated by Godron ‘De l’espèce’ tome 2 page 58 1859, varieties of the carrot growing near each other readily intercross.) A plant of the common parsley was covered by a net, and it apparently produced as many and as fine spontaneously self-fertilised fruits or seeds as the adjoining uncovered plants. The flowers on the latter were visited by so many insects that they must have received pollen from one another. Some of these two lots of seeds were left on sand, but nearly all the self-fertilised seeds germinated before the others, so that I was forced to throw all away. The remaining seeds were then sown on the opposite sides of four pots. At first the self-fertilised seedlings were a little taller in most of the pots than the naturally crossed seedlings, and this no doubt was due to the self-fertilised seeds having germinated first. But in the autumn all the plants were so equal that it did not seem worth while to measure them. In two of the pots they were absolutely equal; in a third, if there was any difference, it was in favour of the crossed plants, and in a somewhat plainer manner in the fourth pot. But neither side had any substantial advantage over the other; so that in height they may be said to be as 100 to 100.
19. DIPSACEAE.—Scabiosa atro-purpurea.
The flowers, which are proterandrous, were fertilised during the unfavourable season of 1867, so that I got few seeds, especially from the self-fertilised heads, which were extremely sterile. The crossed and self-fertilised plants raised from these seeds were measured before they were in full flower, as in Table 5/65.
TABLE 5/65. Scabiosa atro-purpurea.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 14 : 20.
Pot 2 : 15 : 14 4/8.
Pot 3 : 21 : 14. Pot 3 : 18 4/8 : 13.
Total : 68.5 : 61.5.
The four crossed plants averaged 17.12, and the four self-fertilised 15.37 inches in height; or as 100 to 90. One of the self-fertilised plants in Pot 3 was killed by an accident, and its fellow pulled up; so that when they were again measured to the summits of their flowers, there were only three on each side; the crossed now averaged in height 32.83, and the self-fertilised 30.16 inches; or as 100 to 92.
20. COMPOSITAE.—Lactuca sativa. (5/19. The Compositae are well-adapted for cross-fertilisation, but a nurseryman on whom I can rely, told me that he had been in the habit of sowing several kinds of lettuce near together for the sake of seed, and had never observed that they became crossed. It is very improbable that all the varieties which were thus cultivated near together flowered at different times; but two which I selected by hazard and sowed near each other did not flower at the same time; and my trial failed.)
Three plants of Lettuce (Great London Cos var.) grew close together in my garden; one was covered by a net, and produced self-fertilised seeds, the other two were allowed to be naturally crossed by insects; but the season (1867) was unfavourable, and I did not obtain many seeds. Only one crossed and one self-fertilised plant were raised in Pot 1, and their measurements are given in Table 5/66. The flowers on this one self-fertilised plant were again self-fertilised under a net, not with pollen from the same floret, but from other florets on the same head. The flowers on the two crossed plants were left to be crossed by insects, but the process was aided by some pollen being occasionally transported by me from plant to plant. These two lots of seeds, after germinating on sand, were planted in pairs on the opposite sides of Pots 2 and 3, which were at first kept in the greenhouse and then turned out of doors. The plants were measured when in full flower. Table 5/66, therefore, includes plants belonging to two generations. When the seedlings of the two lots were only 5 or 6 inches in height they were equal. In Pot 3 one of the self-fertilised plants died before flowering, as has occurred in so many other cases.
TABLE 5/66. Lactuca sativa.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 27 : 21 4/8. Pot 1 : 25 : 20. First generation, planted in open ground.
Pot 2 : 29 4/8 : 24. Pot 2 : 17 4/8 : 10. Pot 2 : 12 4/8 : 11. Second generation, planted in open ground.
Pot 3 : 14 : 9 4/8. Pot 3 : 10 4/8 : 0. Second generation, kept in the pot.
Total : 136 : 96.
The average height of the seven crossed plants is 19.43, and that of the six self-fertilised plants 16 inches; or as 100 to 82.
21. CAMPANULACEAE.—Specularia speculum.
In the closely allied genus, Campanula, in which Specularia was formerly included, the anthers shed at an early period their pollen, and this adheres to the collecting hairs which surround the pistil beneath the stigma; so that without some mechanical aid the flowers cannot be fertilised. For instance, I covered up a plant of Campanula carpathica, and it did not produce a single capsule, whilst the surrounding uncovered plants seeded profusely. On the other hand, the present species of Specularia appears to set almost as many capsules when covered up, as when left to the visits of the Diptera, which, as far as I have seen, are the only insects that frequent the flowers. (5/20. It has long been known that another species of the genus, Specularia perfoliata, produces cleistogene as well as perfect flowers, and the former are of course self-fertile.) I did not ascertain whether the naturally crossed and spontaneously self-fertilised capsules contained an equal number of seeds, but a comparison of artificially crossed and self-fertilised flowers, showed that the former were probably the most productive. It appears that this plant is capable of producing a large number of self-fertilised capsules owing to the petals closing at night, as well as during cold weather. In the act of closing, the margins of the petals become reflexed, and their inwardly projecting midribs then pass between the clefts of the stigma, and in doing so push the pollen from the outside of the pistil on to the stigmatic surfaces. (5/21. Mr. Meehan has lately shown ‘Proceedings of the Academy of Natural Science Philadelphia’ May 16, 1876 page 84, that the closing of the flowers of Claytonia virginica and Ranunculus bulbosus during the night causes their self-fertilisation.)
Twenty flowers were fertilised by me with their own pollen, but owing to the bad season, only six capsules were produced; they contained on an average 21.7 seeds, with a maximum of forty-eight in one. Fourteen flowers were crossed with pollen from another plant, and these produced twelve capsules, containing on an average 30 seeds, with a maximum in one of fifty-seven seeds; so that the crossed seeds were to the self-fertilised from an equal number of capsules as 100 to 72. The former were also heavier than an equal number of self-fertilised seeds, in the ratio of 100 to 86. Thus, whether we judge by the number of capsules produced from an equal number of flowers, or by the average number of the contained seeds, or the maximum number in any one capsule, or by their weight, crossing does great good in comparison with self-fertilisation. The two lots of seeds were sown on the opposite sides of four pots; but the seedlings were not sufficiently thinned. Only the tallest plant on each side was measured, when fully grown. The measurements are given in Table 5/67. In all four pots the crossed plants flowered first. When the seedlings were only about an inch and a half in height both lots were equal.
TABLE 5/67. Specularia speculum.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Tallest Crossed Plant in each Pot.
Column 3: Tallest Self-fertilised Plant in each Pot.
Pot 1 : 18 : 15 6/8.
Pot 2 : 17 : 19.
Pot 3 : 22 1/8 : 18.
Pot 4 : 20 : 23.
Total : 77.13 : 75.75.
The four tallest crossed plants averaged 19.28, and the four tallest self-fertilised 18.93 inches in height; or as 100 to 98. So that there was no difference worth speaking of between the two lots in height; though other great advantages are derived, as we have seen, from cross-fertilisation. From being grown in pots and kept in the greenhouse, none of the plants produced any capsules.
Lobelia ramosa. (5/22. I have adopted the name given to this plant in the ‘Gardeners’ Chronicle’ 1866. Professor T. Dyer, however, informs me that it probably is a white variety of L. tenuior of R. Brown, from W. Australia.)
The well-adapted means by which cross-fertilisation is ensured in this genus have been described by several authors. (5/23. See the works of Hildebrand and Delpino. Mr. Farrer also has given a remarkably clear description of the mechanism by which cross-fertilisation is effected in this genus, in the ‘Annals and Magazine of Natural History’ volume 2 4th series 1868 page 260. In the allied genus Isotoma, the curious spike which projects rectangularly from the anthers, and which when shaken causes the pollen to fall on the back of an entering insect, seems to have been developed from a bristle, like one of those which spring from the anthers in some of or all the species of Lobelia, as described by Mr. Farrer.) The pistil as it slowly increases in length pushes the pollen out of the conjoined anthers, by the aid of a ring of bristles; the two lobes of the stigma being at this time closed and incapable of fertilisation. The extrusion of the pollen is also aided by insects, which rub against the little bristles that project from the anthers. The pollen thus pushed out is carried by insects to the older flowers, in which the stigma of the now freely projecting pistil is open and ready to be fertilised. I proved the importance of the gaily-coloured corolla, by cutting off the large flowers of Lobelia erinus; and these flowers were neglected by the hive-bees which were incessantly visiting the other flowers.
A capsule was obtained by crossing a flower of L. ramosa with pollen from another plant, and two other capsules from artificially self-fertilised flowers. The contained seeds were sown on the opposite sides of four pots. Some of the crossed seedlings which came up before the others had to be pulled up and thrown away. Whilst the plants were very small there was not much difference in height between the two lots; but in Pot 3 the self-fertilised were for a time the tallest. When in full flower the tallest plant on each side of each pot was measured, and the result is shown in Table 5/68. In all four pots a crossed plant flowered before any one of its opponents.
TABLE 5/68. Lobelia ramosa (First Generation).
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Tallest Crossed Plant in each Pot.
Column 3: Tallest Self-fertilised Plant in each Pot.
Pot 1 : 22 4/8 : 17 4/8.
Pot 2 : 27 4/8 : 24.
Pot 3 : 16 4/8 : 15.
Pot 4 : 22 4/8 : 17.
Total : 89.0 : 73.5.
The four tallest crossed plants averaged 22.25, and the four tallest self-fertilised 18.37 inches in height; or as 100 to 82. I was surprised to find that the anthers of a good many of these self-fertilised plants did not cohere and did not contain any pollen; and the anthers even of a very few of the crossed plants were in the same condition. Some flowers on the crossed plants were again crossed, four capsules being thus obtained; and some flowers on the self-fertilised plants were again self-fertilised, seven capsules being thus obtained. The seeds from both lots were weighed, and it was calculated that an equal number of capsules would have yielded seed in the proportion by weight of 100 for the crossed to 60 for the self-fertilised capsules. So that the flowers on the crossed plants again crossed were much more fertile than those on the self-fertilised plants again self-fertilised.
The above two lots of seeds were placed on damp sand, and many of the crossed seeds germinated, as on the last occasion, before the self-fertilised, and were rejected. Three or four pairs in the same state of germination were planted on the opposite sides of two pots; a single pair in a third pot; and all the remaining seeds were sown crowded in a fourth pot. When the seedlings were about one and a half inches in height, they were equal on both sides of the three first pots; but in Pot 4, in which they grew crowded and were thus exposed to severe competition, the crossed were about a third taller than the self-fertilised. In this latter pot, when the crossed averaged 5 inches in height, the self-fertilised were about 4 inches; nor did they look nearly such fine plants. In all four pots the crossed plants flowered some days before the self-fertilised. When in full flower the tallest plant on each side was measured; but before this time the single crossed plant in Pot 3, which was taller than its antagonist, had died and was not measured. So that only the tallest plant on each side of three pots was measured, as in Table 5/69.
TABLE 5/69. Lobelia ramosa (Second Generation).
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Tallest Crossed Plant in each Pot.
Column 3: Tallest Self-fertilised Plant in each Pot.
Pot 1 : 27 4/8 : 18 4/8.
Pot 2 : 21 : 19 4/8.
Pot 3 : 21 4/8 : 19. Crowded.
Total : 70 : 57.
The average height of the three tallest crossed plants is here 23.33, and that of the tallest self-fertilised 19 inches; or as 100 to 81. Besides this difference in height, the crossed plants were much more vigorous and more branched than the self-fertilised plants, and it is unfortunate that they were not weighed.
Lobelia fulgens.
This species offers a somewhat perplexing case. In the first generation the self-fertilised plants, though few in number, greatly exceeded the crossed in height; whilst in the second generation, when the trial was made on a much larger scale, the crossed beat the self-fertilised plants. As this species is generally propagated by off-sets, some seedlings were first raised, in order to have distinct plants. On one of these plants several flowers were fertilised with their own pollen; and as the pollen is mature and shed long before the stigma of the same flower is ready for fertilisation, it was necessary to number each flower and keep its pollen in paper with a corresponding number. By this means well-matured pollen was used for self-fertilisation. Several flowers on the same plant were crossed with pollen from a distinct individual, and to obtain this the conjoined anthers of young flowers were roughly squeezed, and as it is naturally protruded very slowly by the growth of the pistil, it is probable that the pollen used by me was hardly mature, certainly less mature than that employed for self-fertilisation. I did not at the time think of this source of error, but I now suspect that the growth of the crossed plants was thus injured. Anyhow the trial was not perfectly fair. Opposed to the belief that the pollen used in crossing was not in so good a state as that used for self-fertilisation, is the fact that a greater proportional number of the crossed than of the self-fertilised flowers produced capsules; but there was no marked difference in the amount of seed contained in the capsules of the two lots. (5/24. Gartner has shown that certain plants of Lobelia fulgens are quite sterile with pollen from the same plant, though this pollen is efficient on any other individual; but none of the plants on which I experimented, which were kept in the greenhouse, were in this peculiar condition.)
As the seeds obtained by the above two methods would not germinate when left on bare sand, they were sown on the opposite sides of four pots; but I succeeded in raising only a single pair of seedlings of the same age in each pot. The self-fertilised seedlings, when only a few inches in height, were in most of the pots taller than their opponents; and they flowered so much earlier in all the pots, that the height of the flower-stems could be fairly compared only in Pots 1 and 2.
TABLE 5/70. Lobelia fulgens (First Generation).
Heights of flower-stems measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Height of Flower-stems on the Crossed Plants.
Column 3: Height of Flower-stems on the Self-fertilised Plants.
Pot 1 : 33 : 50.
Pot 2 : 36 4/8 : 38 4/8.
Pot 3 : 21* : 43.
Pot 4 : 12* : 35 6/8.
*Not in full flower.
The mean height of the flower-stems of the two crossed plants in Pots 1 and 2 is here 34.75 inches, and that of the two self-fertilised plants in the same pots 44.25 inches; or as 100 to 127. The self-fertilised plants in Pots 3 and 4 were in every respect very much finer than the crossed plants.
I was so much surprised at this great superiority of the self-fertilised over the crossed plants, that I determined to try how they would behave in one of the pots during a second growth. The two plants, therefore, in Pot 1 were cut down, and repotted without being disturbed in a much larger pot. In the following year the self-fertilised plant showed even a greater superiority than before; for the two tallest flower-stems produced by the one crossed plant were only 29 4/8 and 30 1/8 inches in height, whereas the two tallest stems on the one self-fertilised plant were 49 4/8 and 49 6/8 inches; and this gives a ratio of 100 to 167. Considering all the evidence, there can be no doubt that these self-fertilised plants had a great superiority over the crossed plants.
TABLE 5/71. Lobelia fulgens (Second Generation).
Heights of flower-stems measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 27 3/8 : 32 3/8. Pot 1 : 26 : 26 3/8. Pot 1 : 24 3/8 : 25 1/8. Pot 1 : 24 4/8 : 26 2/8.
Pot 2 : 34 : 36 2/8. Pot 2 : 26 6/8 : 28 6/8. Pot 2 : 25 1/8 : 30 1/8. Pot 2 : 26 : 32 2/8.
Pot 3 : 40 4/8 : 30 4/8. Pot 3 : 37 5/8 : 28 2/8. Pot 3 : 32 1/8 : 23.
Pot 4 : 34 5/8 : 29 4/8. Pot 4 : 32 2/8 : 28 3/8. Pot 4 : 29 3/8 : 26. Pot 4 : 27 1/8 : 25 2/8.
Pot 5 : 28 1/8 : 29. Pot 5 : 27 : 24 6/8. Pot 5 : 25 3/8 : 23 2/8. Pot 5 : 24 3/8 : 24.
Pot 6 : 33 5/8 : 44 2/8. Pot 6 : 32 : 37 6/8. Pot 6 : 26 1/8 : 37. Pot 6 : 25 : 35.
Pot 7 : 30 6/8 : 27 2/8. Pot 7 : 30 3/8 : 19 2/8. Pot 7 : 29 2/8 : 21.
Pot 8 : 39 3/8 : 23 1/8. Pot 8 : 37 2/8 : 23 4/8. Pot 8 : 36 : 25 4/8. Pot 8 : 36 : 25 1/8.
Pot 9 : 33 3/8 : 19 3/8. Pot 9 : 25 : 16 3/8. Pot 9 : 25 3/8 : 19. Pot 9 : 21 7/8 : 18 6/8.
Total : 1014.00 : 921.63.
I determined on this occasion to avoid the error of using pollen of not quite equal maturity for crossing and self-fertilisation; so that I squeezed pollen out of the conjoined anthers of young flowers for both operations. Several flowers on the crossed plant in Pot 1 in Table 5/70 were again crossed with pollen from a distinct plant. Several other flowers on the self-fertilised plant in the same pot were again self-fertilised with pollen from the anthers of other flowers on the SAME PLANT. Therefore the degree of self-fertilisation was not quite so close as in the last generation, in which pollen from the SAME FLOWER, kept in paper, was used. These two lots of seeds were thinly sown on opposite sides of nine pots; and the young seedlings were thinned, an equal number of nearly as possible the same age being left on the two sides. In the spring of the following year (1870), when the seedlings had grown to a considerable size, they were measured to the tips of their leaves; and the twenty-three crossed plants averaged 14.04 inches in height, whilst the twenty-three self-fertilised seedlings were 13.54 inches; or as 100 to 96.
In the summer of the same year several of these plants flowered, the crossed and self-fertilised plants flowering almost simultaneously, and all the flower-stems were measured. Those produced by eleven of the crossed plants averaged 30.71 inches, and those by nine of the self-fertilised plants 29.43 inches in height; or as 100 to 96.
The plants in these nine pots, after they had flowered, were repotted without being disturbed in much larger pots; and in the following year, 1871, all flowered freely; but they had grown into such an entangled mass, that the separate plants on each side could no longer be distinguished. Accordingly three or four of the tallest flower-stems on each side of each pot were measured; and the measurements in Table 5/71 are, I think, more trustworthy than the previous ones, from being more numerous, and from the plants being well established and growing vigorously.
The average height of the thirty-four tallest flower-stems on the twenty-three crossed plants is 29.82 inches, and that of the same number of flower-stems on the same number of self-fertilised plants is 27.10 inches, or as 100 to 91. So that the crossed plants now showed a decided advantage over their self-fertilised opponents.
22. POLEMONIACEAE.—Nemophila insignis.
Twelve flowers were crossed with pollen from a distinct plant, but produced only six capsules, containing on an average 18.3 seeds. Eighteen flowers were fertilised with their own pollen and produced ten capsules, containing on an average 12.7 seeds, so that the seeds per capsule were as 100 to 69. (5/25. Several species of Polemoniaceae are known to be proterandrous, but I did not attend to this point in Nemophila. Verlot says ‘Des Variétés’ 1865 page 66, that varieties growing near one another spontaneously intercross.) The crossed seeds weighed a little less than an equal number of self-fertilised seeds, in the proportion of 100 to 105; but this was clearly due to some of the self-fertilised capsules containing very few seeds, and these were much bulkier than the others, from having been better nourished. A subsequent comparison of the number of seeds in a few capsules did not show so great a superiority on the side of the crossed capsules as in the present case.
The seeds were placed on sand, and after germinating were planted in pairs on the opposite sides of five pots, which were kept in the greenhouse. When the seedlings were from 2 to 3 inches in height, most of the crossed had a slight advantage over the self-fertilised. The plants were trained up sticks, and thus grew to a considerable height. In four out of the five pots a crossed plant flowered before any one of the self-fertilised. The plants were first measured to the tips of their leaves, before they had flowered and when the crossed were under a foot in height. The twelve crossed plants averaged 11.1 inches in height, whilst the twelve self-fertilised were less than half of this height, namely, 5.45; or as 100 to 49. Before the plants had grown to their full height, two of the self-fertilised died, and as I feared that this might happen with others, they were again measured to the tops of their stems, as shown in Table 5/72.
TABLE 5/72. Nemophila insignis; 0 means that the plant died.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 32 4/8 : 21 2/8.
Pot 2 : 34 4/8 : 23 5/8.
Pot 3 : 33 1/8 : 19. Pot 3 : 22 2/8 : 7 2/8. Pot 3 : 29 : 17 4/8.
Pot 4 : 35 4/8 : 10 4/8. Pot 4 : 33 4/8 : 27.
Pot 5 : 35 : 0. Pot 5 : 38 : 18 3/8. Pot 5 : 36 : 20 4/8. Pot 5 : 37 4/8 : 34. Pot 5 : 32 4/8 : 0.
Total : 399.38 : 199.00.
The twelve crossed plants now averaged 33.28, and the ten self-fertilised 19.9 inches in height, or as 100 to 60; so that they differed somewhat less than before.
The plants in Pots 3 and 5 were placed under a net in the greenhouse, two of the crossed plants in the latter pot being pulled up on account of the death of two of the self-fertilised; so that altogether six crossed and six self-fertilised plants were left to fertilise themselves spontaneously. The pots were rather small, and the plants did not produce many capsules. The small size of the self-fertilised plants will largely account for the fewness of the capsules which they produced. The six crossed plants bore 105, and the six self-fertilised only 30 capsules; or as 100 to 29.
The self-fertilised seeds thus obtained from the crossed and self-fertilised plants, after germinating on sand, were planted on the opposite sides of four small pots, and treated as before. But many of the plants were unhealthy, and their heights were so unequal—some on both sides being five times as tall as the others—that the averages deduced from the measurements in Table 5/73 are not in the least trustworthy. Nevertheless I have felt bound to give them, as they are opposed to my general conclusions.
The seven self-fertilised plants from the crossed plants here average 15.73, and the seven self-fertilised from the self-fertilised 21 inches in height; or as 100 to 133. Strictly analogous experiments with Viola tricolor and Lathyrus odoratus gave a very different result.
TABLE 5/73. Nemophila insignis.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Self-fertilised Plants from Crossed Plants.
Column 3: Self-fertilised Plants from Self-fertilised Plants.
Pot 1 : 27 : 27 4/8. Pot 1 : 14 : 34 2/8.
Pot 2 : 17 6/8 : 23. Pot 2 : 24 4/8 : 32.
Pot 3 : 16 : 7.
Pot 4 : 5 3/8 : 7 2/8. Pot 4 : 5 4/8 : 16.
Total : 110.13 : 147.00.
23. BORAGINACEAE.—Borago officinalis.
This plant is frequented by a greater number of bees than any other one which I have observed. It is strongly proterandrous (H. Muller ‘Befruchtung’ etc. page 267), and the flowers can hardly fail to be cross-fertilised; but should this not occur, they are capable of self-fertilisation to a limited extent, as some pollen long remains within the anthers, and is apt to fall on the mature stigma. In the year 1863 I covered up a plant, and examined thirty-five flowers, of which only twelve yielded any seeds; whereas of thirty-five flowers on an exposed plant growing close by, all with the exception of two yielded seeds. The covered-up plant, however, produced altogether twenty-five spontaneously self-fertilised seeds; the exposed plant producing fifty-five seeds, the product, no doubt, of cross-fertilisation.
In the year 1868 eighteen flowers on a protected plant were crossed with pollen from a distinct plant, but only seven of these produced fruit; and I suspect that I applied pollen to many of the stigmas before they were mature. These fruits contained on an average 2 seeds, with a maximum in one of three seeds. Twenty-four spontaneously self-fertilised fruits were produced by the same plant, and these contained on an average 1.2 seeds, with a maximum of two in one fruit. So that the fruits from the artificially crossed flowers yielded seeds compared with those from the spontaneously self-fertilised flowers, in the ratio of 100 to 60. But the self-fertilised seeds, as often occurs when few are produced, were heavier than the crossed seeds in the ratio of 100 to 90.
These two lots of seeds were sown on opposite sides of two large pots; but I succeeded in raising only four pairs of equal age. When the seedlings on both sides were about 8 inches in height they were equal. When in full flower they were measured, as follows:—
TABLE 5/74. Borago officinalis.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 19 : 13 4/8. Pot 1 : 21 : 18 6/8. Pot 1 : 16 4/8 : 20 2/8.
Pot 2 : 26 2/8 : 32 2/8.
Total : 82.75 : 84.75.
The average height of the four crossed plants is here 20.68, and that of the four self-fertilised 21.18 inches; or as 100 to 102. The self-fertilised plants thus exceeded the crossed in height by a little; but this was entirely due to the tallness of one of the self-fertilised. The crossed plants in both pots flowered before the self-fertilised. Therefore I believe if more plants had been raised, the result would have been different. I regret that I did not attend to the fertility of the two lots.
24. NOLANACEAE.—Nolana prostrata.
In some of the flowers the stamens are considerably shorter than the pistil, in others equal to it in length. I suspected, therefore, but erroneously as it proved, that this plant was dimorphic, like Primula, Linum, etc., and in the year 1862 twelve plants, covered by a net in the greenhouse, were subjected to trial. The spontaneously self-fertilised flowers yielded 64 grains weight of seeds, but the product of fourteen artificially crossed flowers is here included, which falsely increases the weight of the self-fertilised seeds. Nine uncovered plants, the flowers of which were eagerly visited by bees for their pollen and were no doubt intercrossed by them, produced 79 grains weight of seeds: therefore twelve plants thus treated would have yielded 105 grains. Thus the seeds produced by the flowers on an equal number of plants, when crossed by bees, and spontaneously self-fertilised (the product of fourteen artificially crossed flowers being, however, included in the latter) were in weight as 100 to 61.
In the summer of 1867 the trial was repeated; thirty flowers were crossed with pollen from a distinct plant and produced twenty-seven capsules, each containing five seeds. Thirty-two flowers were fertilised with their own pollen, and produced only six capsules, each with five seeds. So that the crossed and self-fertilised capsules contained the same number of seeds, though many more capsules were produced by the cross-fertilised than by the self-fertilised flowers, in the ratio of 100 to 21.
An equal number of seeds of both lots were weighed, and the crossed seeds were to the self-fertilised in weight as 100 to 82. Therefore a cross increases the number of capsules produced and the weight of the seeds, but not the number of seeds in each capsule.
These two lots of seeds, after germinating on sand, were planted on the opposite sides of three pots. The seedlings when from 6 to 7 inches in height were equal. The plants were measured when fully grown, but their heights were so unequal in the several pots, that the result cannot be fully trusted.
TABLE 5/75. Nolana prostrata.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 8 4/8 : 4 2/8. Pot 1 : 6 4/8 : 7 4/8.
Pot 2 : 10 4/8 : 14 4/8. Pot 2 : 18 : 18.
Pot 3 : 20 2/8 : 22 6/8.
Total : 63.75 : 67.00.
The five crossed plants average 12.75, and the five self-fertilised 13.4 inches in height; or as 100 to 105.