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I. INTRODUCTORY REMARKS.
I. INTRODUCTORY REMARKS.
Various means which favour or determine the cross-fertilisation of plants.—Benefits derived from cross-fertilisation.—Self-fertilisation favourable to the propagation of the species.—Brief history of the subject.—Object of the experiments, and the manner in which they were tried.—Statistical value of the measurements.—The experiments carried on during several successive generations.—Nature of the relationship of the plants in the later generations.—Uniformity of the conditions to which the plant
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II. CONVOLVULACEAE.
II. CONVOLVULACEAE.
Ipomoea purpurea, comparison of the height and fertility of the crossed and self-fertilised plants during ten successive generations.—Greater constitutional vigour of the crossed plants.—The effects on the offspring of crossing different flowers on the same plant, instead of crossing distinct individuals.—The effects of a cross with a fresh stock.—The descendants of the self-fertilised plant named Hero.—Summary on the growth, vigour, and fertility of the successive crossed and self-fertilised ge
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III. SCROPHULARIACEAE, GESNERIACEAE, LABIATAE, ETC.
III. SCROPHULARIACEAE, GESNERIACEAE, LABIATAE, ETC.
Mimulus luteus; height, vigour, and fertility of the crossed and self-fertilised plants of the first four generations.—Appearance of a new, tall, and highly self-fertile variety.—Offspring from a cross between self-fertilised plants.—Effects of a cross with a fresh stock.—Effects of crossing flowers on the same plant.—Summary on Mimulus luteus.—Digitalis purpurea, superiority of the crossed plants.—Effects of crossing flowers on the same plant.—Calceolaria.—Linaria vulgaris.—Verbascum thapsus.—V
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IV. CRUCIFERAE, PAPAVERACEAE, RESEDACEAE, ETC.
IV. CRUCIFERAE, PAPAVERACEAE, RESEDACEAE, ETC.
Brassica oleracea, crossed and self-fertilised plants.—Great effect of a cross with a fresh stock on the weight of the offspring.—Iberis umbellata.—Papaver vagum.—Eschscholtzia californica, seedlings from a cross with a fresh stock not more vigorous, but more fertile than the self-fertilised seedlings.—Reseda lutea and odorata, many individuals sterile with their own pollen.—Viola tricolor, wonderful effects of a cross.—Adonis aestivalis.—Delphinium consolida.—Viscaria oculata, crossed plants ha
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V. GERANIACEAE, LEGUMINOSAE, ONAGRACEAE, ETC.
V. GERANIACEAE, LEGUMINOSAE, ONAGRACEAE, ETC.
Pelargonium zonale, a cross between plants propagated by cuttings does no good.—Tropaeolum minus.—Limnanthes douglasii.—Lupinus luteus and pilosus.—Phaseolus multiflorus and vulgaris.—Lathyrus odoratus, varieties of, never naturally intercross in England.—Pisum sativum, varieties of, rarely intercross, but a cross between them highly beneficial.—Sarothamnus scoparius, wonderful effects of a cross.—Ononis minutissima, cleistogene flowers of.—Summary on the Leguminosae.—Clarkia elegans.—Bartonia a
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VI. SOLANACEAE, PRIMULACEAE, POLYGONEAE, ETC.
VI. SOLANACEAE, PRIMULACEAE, POLYGONEAE, ETC.
Petunia violacea, crossed and self-fertilised plants compared for four generations.—Effects of a cross with a fresh stock.—Uniform colour of the flowers on the self-fertilised plants of the fourth generation.—Nicotiana tabacum, crossed and self-fertilised plants of equal height.—Great effects of a cross with a distinct sub-variety on the height, but not on the fertility, of the offspring.—Cyclamen persicum, crossed seedlings greatly superior to the self-fertilised.—Anagallis collina.—Primula ver
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VII.
VII.
A SUMMARY OF THE HEIGHTS AND WEIGHTS OF THE CROSSED AND SELF-FERTILISED PLANTS. Number of species and plants measured.—Tables given.—Preliminary remarks on the offspring of plants crossed by a fresh stock.—Thirteen cases specially considered.—The effects of crossing a self-fertilised plant either by another self-fertilised plant or by an intercrossed plant of the old stock.—Summary of the results.—Preliminary remarks on the crossed and self-fertilised plants of the same stock.—The twenty-six exc
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VIII.
VIII.
DIFFERENCE BETWEEN CROSSED AND SELF-FERTILISED PLANTS IN CONSTITUTIONAL VIGOUR AND IN OTHER RESPECTS. Greater constitutional vigour of crossed plants.—The effects of great crowding.—Competition with other kinds of plants.—Self-fertilised plants more liable to premature death.—Crossed plants generally flower before the self-fertilised.—Negative effects of intercrossing flowers on the same plant.—Cases described.—Transmission of the good effects of a cross to later generations.—Effects of crossing
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IX.
IX.
THE EFFECTS OF CROSS-FERTILISATION AND SELF-FERTILISATION ON THE PRODUCTION OF SEEDS. Fertility of plants of crossed and self-fertilised parentage, both lots being fertilised in the same manner.—Fertility of the parent-plants when first crossed and self-fertilised, and of their crossed and self-fertilised offspring when again crossed and self-fertilised.—Comparison of the fertility of flowers fertilised with their own pollen and with that from other flowers on the same plant.—Self-sterile plants
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X. MEANS OF FERTILISATION.
X. MEANS OF FERTILISATION.
Sterility and fertility of plants when insects are excluded.—The means by which flowers are cross-fertilised.—Structures favourable to self-fertilisation.—Relation between the structure and conspicuousness of flowers, the visits of insects, and the advantages of cross-fertilisation.—The means by which flowers are fertilised with pollen from a distinct plant.—Greater fertilising power of such pollen.—Anemophilous species.—Conversion of anemophilous species into entomophilous.—Origin of nectar.—An
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XI. THE HABITS OF INSECTS IN RELATION TO THE FERTILISATION OF FLOWERS.
XI. THE HABITS OF INSECTS IN RELATION TO THE FERTILISATION OF FLOWERS.
Insects visit the flowers of the same species as long as they can.—Cause of this habit.—Means by which bees recognise the flowers of the same species.—Sudden secretion of nectar.—Nectar of certain flowers unattractive to certain insects.—Industry of bees, and the number of flowers visited within a short time.—Perforation of the corolla by bees.—Skill shown in the operation.—Hive-bees profit by the holes made by humble-bees.—Effects of habit.—The motive for perforating flowers to save time.—Flowe
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XII. GENERAL RESULTS.
XII. GENERAL RESULTS.
Cross-fertilisation proved to be beneficial, and self-fertilisation injurious.—Allied species differ greatly in the means by which cross-fertilisation is favoured and self-fertilisation avoided.—The benefits and evils of the two processes depend on the degree of differentiation in the sexual elements.—The evil effects not due to the combination of morbid tendencies in the parents.—Nature of the conditions to which plants are subjected when growing near together in a state of nature or under cult
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THE EFFECTS OF CROSS AND SELF-FERTILISATION IN THE VEGETABLE KINGDOM.
THE EFFECTS OF CROSS AND SELF-FERTILISATION IN THE VEGETABLE KINGDOM.
There is weighty and abundant evidence that the flowers of most kinds of plants are constructed so as to be occasionally or habitually cross-fertilised by pollen from another flower, produced either by the same plant, or generally, as we shall hereafter see reason to believe, by a distinct plant. Cross-fertilisation is sometimes ensured by the sexes being separated, and in a large number of cases by the pollen and stigma of the same flower being matured at different times. Such plants are called
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TABLE 1/2.
TABLE 1/2.
Column 1: Number (Name) of Pot. Column 2: Crossed. Column 3: Self-fertilised. Column 4: Difference. Pot 1 : 18 7/8 : 19 2/8 : +0 3/8. Pot 2 : 20 7/8 : 19 : -1 7/8. Pot 3 : 21 1/8 : 16 7/8 : -4 2/8. Pot 4 : 19 6/8 : 16 : -3 6/8. “Next as regards the numerical estimate of this excess. The mean values of the several groups are so discordant, as is shown in Table 1/2, that a fairly precise numerical estimate seems impossible. But the consideration arises, whether the difference between pot and pot m
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ON SOME APPARENT AND REAL CAUSES OF ERROR IN MY EXPERIMENTS.
ON SOME APPARENT AND REAL CAUSES OF ERROR IN MY EXPERIMENTS.
It has been objected to such experiments as mine, that covering plants with a net, although only for a short time whilst in flower, may affect their health and fertility. I have seen no such effect except in one instance with a Myosotis, and the covering may not then have been the real cause of injury. But even if the net were slightly injurious, and certainly it was not so in any high degree, as I could judge by the appearance of the plants and by comparing their fertility with that of neighbou
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
Flowers on the crossed plants of the last generation (Table 2/1) were crossed by pollen from distinct plants of the same generation; and flowers on the self-fertilised plants were fertilised by pollen from the same flower. The seeds thus produced were treated in every respect as before, and we have in Table 2/2 the result. TABLE 2/2. Ipomoea purpurea (Second Generation.). Heights of Plants in inches: Column 1: Number (Name) of Pot. Column 2: Crossed Plants. Column 3: Self-fertilised Plants. Pot
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CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
Seeds from the crossed plants of the last generation (Table 2/2) again crossed, and from the self-fertilised plants again self-fertilised, were treated in all respects exactly as before, with the following result:— TABLE 2/3. Ipomoea purpurea (Third Generation.). Heights of Plants in inches: Column 1: Number (Name) of Pot. Column 2: Crossed Plants. Column 3: Self-fertilised Plants. Pot 1 : 74 : 56 4/8. Pot 1 : 72 : 51 4/8. Pot 1 : 73 4/8 : 54. Pot 2 : 82 : 59. Pot 2 : 81 : 30. Pot 2 : 82 : 66. T
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CROSSED AND SELF-FERTILISED PLANTS OF THE FOURTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE FOURTH GENERATION.
Seedlings raised as before from the crossed and self-fertilised plants of the third generation in Table 2/3, gave results as follows:— TABLE 2/5. Ipomoea purpurea (Fourth Generation). Heights of Plants in inches: Column 1: Number (Name) of Pot. Column 2: Crossed Plants. Column 3: Self-fertilised Plants. Pot 1 : 84 : 80. Pot 1 : 47 : 44 1/2. Pot 2 : 83 : 73 1/2. Pot 2 : 59 : 51 1/2. Pot 3 : 82 : 56 1/2. Pot 3 : 65 1/2 : 63. Pot 3 : 68 : 52. Total : 488.5 : 421.0. Here the average height of the se
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CROSSED AND SELF-FERTILISED PLANTS OF THE FIFTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE FIFTH GENERATION.
These were raised in the same manner as before, and when measured gave the following results:— TABLE 2/6. Ipomoea purpurea (Fifth Generation). Heights of Plants in inches: Column 1: Number (Name) of Pot. Column 2: Crossed Plants. Column 3: Self-fertilised Plants. Pot 1 : 96 : 73. Pot 1 : 86 : 78. Pot 1 : 69 : 29. Pot 2 : 84 : 51. Pot 2 : 84 : 84. Pot 2 : 76 1/4 : 59. Total : 495.25 : 374.00. The average height of the six crossed plants is 82.54 inches, and that of the six self-fertilised plants
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CROSSED AND SELF-FERTILISED PLANTS OF THE SIXTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SIXTH GENERATION.
These were raised in the usual manner, with the following result. I should state that there were originally eight plants on each side; but as two of the self-fertilised became extremely unhealthy and never grew to near their full height, these as well as their opponents have been struck out of the list. If they had been retained, they would have made the average height of the crossed plants unfairly greater than that of the self-fertilised. I have acted in the same manner in a few other instance
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CROSSED AND SELF-FERTILISED PLANTS OF THE SEVENTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SEVENTH GENERATION.
These were raised as heretofore with the following result:— TABLE 2/8. Ipomoea purpurea (Seventh Generation). Heights of Plants in inches: Column 1: Number (Name) of Pot. Column 2: Crossed Plants. Column 3: Self-fertilised Plants. Pot 1 : 84 4/8 : 74 6/8. Pot 1 : 84 6/8 : 84. Pot 1 : 76 2/8 : 55 4/8. Pot 2 : 84 4/8 : 65. Pot 2 : 90 : 51 2/8. Pot 2 : 82 2/8 : 80 4/8. Pot 3 : 83 : 67 6/8. Pot 3 : 86 : 60 2/8. Pot 4 : 84 2/8 : 75 2/8. Total : 755.50 : 614.25. Each of these nine crossed plants is hi
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CROSSED AND SELF-FERTILISED PLANTS OF THE EIGHTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE EIGHTH GENERATION.
As just stated, the plants of the last generation, from which the present ones were raised, were very unhealthy and their seeds of unusually small size; and this probably accounts for the two lots behaving differently to what they did in any of the previous or succeeding generations. Many of the self-fertilised seeds germinated before the crossed ones, and these were of course rejected. When the crossed seedlings in Table 2/9 had grown to a height of between 1 and 2 feet, they were all, or almos
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CROSSED AND SELF-FERTILISED PLANTS OF THE NINTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE NINTH GENERATION.
The plants of this generation were raised in the same manner as before, with the result shown in Table 2/10. The fourteen crossed plants average in height 81.39 inches and the fourteen self-fertilised plants 64.07, or as 100 to 79. One self-fertilised plant in Pot 3 exceeded, and one in Pot 4 equalled in height, its opponent. The self-fertilised plants showed no sign of inheriting the precocious growth of their parents; this having been due, as it would appear, to the abnormal state of the seeds
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CROSSED AND SELF-FERTILISED PLANTS OF THE TENTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE TENTH GENERATION.
Six plants were raised in the usual manner from the crossed plants of the last generation (Table 2/10) again intercrossed, and from the self-fertilised again self-fertilised. As one of the crossed plants in Pot 1 in Table 2/11 became much diseased, having crumpled leaves, and producing hardly any capsules, it and its opponent have been struck out of the table. TABLE 2/11. Ipomoea purpurea (Tenth Generation). Heights of Plants in inches: Column 1: Number (Name) of Pot. Column 2: Crossed Plants. C
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THIRD GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
THIRD GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
Crossed capsules compared with self-fertilised capsules contained seeds in the ratio of : 100 to 94. An equal number of crossed and self-fertilised plants, both spontaneously self-fertilised, produced capsules in the ratio of : 100 to 38. And these capsules contained seeds in the ratio of : 100 to 94. Combining these data, the productiveness of the crossed to the self-fertilised plants, both spontaneously self-fertilised, was as : 100 to 35....
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FOURTH GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
FOURTH GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
Capsules from flowers on the crossed plants fertilised by pollen from another plant, and capsules from flowers on the self-fertilised plants fertilised with their own pollen, contained seeds in the proportion of : 100 to 94....
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FIFTH GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
FIFTH GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
The crossed plants produced spontaneously a vast number more pods (not actually counted) than the self-fertilised, and these contained seeds in the proportion of : 100 to 89....
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NINTH GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
NINTH GENERATION OF CROSSED AND SELF-FERTILISED PLANTS.
Fourteen crossed plants, spontaneously self-fertilised, and fourteen self-fertilised plants spontaneously self-fertilised, yielded capsules (the average number of seeds per capsule not having been ascertained) in the proportion of : 100 to 26. PLANTS DERIVED FROM A CROSSED WITH A FRESH STOCK COMPARED WITH INTERCROSSED PLANTS. The offspring of intercrossed plants of the ninth generation, crossed by a fresh stock, compared with plants of the same stock intercrossed during ten generations, both set
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CROSSED AND SELF-FERTILISED PLANTS OF THE FIRST GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE FIRST GENERATION.
Having ascertained, by leaving crossed and self-fertilised seed on damp sand, that they germinated simultaneously, both kinds were thickly sown on opposite sides of a broad and rather shallow pan; so that the two sets of seedlings, which came up at the same time, were subjected to the same unfavourable conditions. This was a bad method of treatment, but this species was one of the first on which I experimented. When the crossed seedlings were on an average half an inch high, the self-fertilised
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
Seeds from the foregoing plants, fertilised in the manner just stated, were sown on the opposite sides of a small pot (1) and came up crowded. The four tallest crossed seedlings, at the time of flowering, averaged 8 inches in height, whilst the four tallest self-fertilised plants averaged only 4 inches. Crossed seeds were sown by themselves in a second small pot, and self-fertilised seeds were sown by themselves in a third small pot so that there was no competition whatever between these two lot
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CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
Crossed seeds from the crossed plants, and self-fertilised seeds from the self-fertilised plants of the last generation, were sown thickly on opposite sides of a small pot, Number 1. The two tallest plants on each side were measured after they had flowered, and the two crossed ones were 12 and 7 1/2 inches, and the two self-fertilised ones 8 and 5 1/2 inches in height; that is, in the ratio of 100 to 69. Twenty flowers on the crossed plants were again crossed and produced twenty capsules; ten of
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CROSSED AND SELF-FERTILISED PLANTS OF THE FOURTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE FOURTH GENERATION.
Seeds of the two kinds, produced in the usual way from the two sets of plants of the third generation, were sown on opposite sides of two pots (1 and 2); but the seedlings were not thinned enough and did not grow well. Many of the self-fertilised plants, especially in one of the pots, consisted of the new and tall variety above referred to, which bore large and almost white flowers marked with crimson blotches. I will call it the WHITE VARIETY. I believe that it first appeared amongst both the c
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CROSSED AND SELF-FERTILISED PLANTS OF THE FIFTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE FIFTH GENERATION.
Seeds from both lots of the fourth generation, fertilised in the usual manner, were sown on opposite sides of three pots. When the seedlings flowered, most of the self-fertilised plants were found to consist of the tall white variety. Several of the crossed plants in Pot 1 likewise belonged to this variety, as did a very few in Pots 2 and 3. The tallest crossed plant in Pot 1 was 7 inches, and the tallest self-fertilised plant on the opposite side 8 inches; in Pots 2 and 3 the tallest crossed we
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CROSSED AND SELF-FERTILISED PLANTS OF THE SIXTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SIXTH GENERATION.
Seeds from plants of the fifth generation crossed and self-fertilised in the usual manner were sown on opposite sides of several pots. On the self-fertilised side every single plant belonged to the tall white variety. On the crossed side some plants belonged to this variety, but the greater number approached in character to the old and shorter kinds with smaller yellowish flowers blotched with coppery brown. When the plants on both sides were from 2 to 3 inches in height they were equal, but whe
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CROSSED AND SELF-FERTILISED PLANTS OF THE SEVENTH GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SEVENTH GENERATION.
Crossed and self-fertilised seeds from the crossed and self-fertilised plants of the sixth generation were sown in the usual manner on opposite sides of three pots, and the seedlings were well and equally thinned. Every one of the self-fertilised plants (and many were raised) in this, as well as in the eighth and ninth generations, belonged to the tall white variety. Their uniformity of character, in comparison with the seedlings first raised from the purchased seed, was quite remarkable. On the
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THE EFFECTS OF A CROSS WITH A DISTINCT STOCK.
THE EFFECTS OF A CROSS WITH A DISTINCT STOCK.
Some flowers on the self-fertilised plants in Pot 4 in Table 3/19 were fertilised with their own pollen, and plants of the eighth self-fertilised generation were thus raised, merely to serve as parents in the following experiment. Several flowers on these plants were allowed to fertilise themselves spontaneously (insects being of course excluded), and the plants raised from these seeds formed the ninth self-fertilised generation; they consisted wholly of the tall white variety with crimson blotc
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CALCEOLARIA. A BUSHY GREENHOUSE VARIETY, WITH YELLOW FLOWERS BLOTCHED WITH PURPLE.
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, how
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VAR. CATTELL’S EARLY BARNES CABBAGE.
VAR. CATTELL’S EARLY BARNES CABBAGE.
The flowers of the common cabbage are adapted, as shown by H. Muller, for cross-fertilisation, and should this fail, for self-fertilisation. (4/1. ‘Die Befruchtung’ etc. page 139.) It is well known that the varieties are crossed so largely by insects, that it is impossible to raise pure kinds in the same garden, if more than one kind is in flower at the same time. Cabbages, in one respect, were not well fitted for my experiments, as, after they had formed heads, they were often difficult to meas
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
Some flowers on the crossed plants of the last generation were again crossed with pollen from another crossed plant, and produced fine capsules. The flowers on the self-fertilised plants of the last generation were allowed to fertilise themselves spontaneously under a net, and they produced some remarkably fine capsules. The two lots of seeds thus produced germinated on sand, and eight pairs were planted on opposite sides of four pots. These plants were measured to the tips of their leaves on th
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THE EFFECTS OF A CROSS WITH A FRESH STOCK.
THE EFFECTS OF A CROSS WITH A FRESH STOCK.
Some flowers on a crossed plant of the last or second generation were fertilised, without being castrated, by pollen taken from a plant of the same variety, but not related to my plants, and brought from a nursery garden (whence my seeds originally came) having a different soil and aspect. The flowers on the self-fertilised plants of the last or second generation (Table 4/29) were allowed to fertilise themselves spontaneously under a net, and yielded plenty of seeds. These latter and the crossed
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VAR. KERMESIANA.
VAR. KERMESIANA.
This variety produced plenty of spontaneously self-fertilised seed under a net. Other plants in pots in the greenhouse were left uncovered, and as I saw small flies visiting the flowers, it seemed probable that they would be intercrossed. Consequently seeds supposed to have been thus crossed and spontaneously self-fertilised seeds were sown on opposite sides of a pot. The self-fertilised seedlings grew from the first quicker than the supposed crossed seedlings, and when both lots were in full fl
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CROSS BY A FRESH STOCK.
CROSS BY A FRESH STOCK.
From the doubts caused by the two first trials, in which it was not known with certainty that the plants had been crossed; and from the crossed plants in the last experiment having been put into competition with plants self-fertilised for three generations, which moreover grew very unequally, I resolved to repeat the trial on a larger scale, and in a rather different manner. I obtained seeds of the same crimson variety of Iberis umbellata from another nursery garden, and raised plants from them.
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
The fact just given with respect to the growth of the cut-down plants made me doubtful about my first trial, so I determined to make another on a larger scale with crossed and self-fertilised seedlings raised from the crossed and self-fertilised plants of the last generation. Eleven pairs were raised and grown in competition in the usual manner; and now the result was different, for the two lots were nearly equal during their whole growth. It would therefore be superfluous to give a table of the
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PLANTS RAISED FROM BRAZILIAN SEED.
PLANTS RAISED FROM BRAZILIAN SEED.
Fritz Muller sent me from South Brazil seeds of plants which were there absolutely sterile when fertilised with pollen from the same plant, but were perfectly fertile when fertilised with pollen from any other plant. The plants raised by me in England from these seeds were examined by Professor Asa Gray, and pronounced to belong to E. Californica, with which they were identical in general appearance. Two of these plants were covered by a net, and were found not to be so completely self-sterile a
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THE EFFECTS OF A CROSS WITH A FRESH STOCK.
THE EFFECTS OF A CROSS WITH A FRESH STOCK.
I now tried a different experiment. Eight flowers on the self-fertilised plants of the last experiment (i.e., grandchildren of the plants which grew in Brazil) were again fertilised with pollen from the same plant, and produced five capsules, containing on an average 27.4 seeds, with a maximum in one of forty-two seeds. The seedlings raised from these seeds formed the second SELF-FERTILISED generation of the Brazilian stock. Eight flowers on one of the crossed plants of the last experiment were
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CROSSED AND SELF-FERTILISED PLANTS OF THE FIRST GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE FIRST GENERATION.
The many seeds obtained from the above crossed and artificially self-fertilised flowers were sown out of doors, and two large beds of seedlings, closely adjoining one another, thus raised. This was the first plant on which I experimented, and I had not then formed any regular scheme of operation. When the two lots were in full flower, I measured roughly a large number of plants but record only that the crossed were on an average fully 4 inches taller than the self-fertilised. Judging from subseq
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
The crossed and self-fertilised seeds from the crossed and self-fertilised plants of the last generation were sown on opposite sides of two pots; but the seedlings were not thinned enough, so that both lots grew very irregularly, and most of the self-fertilised plants after a time died from being smothered. My measurements were, therefore, very incomplete. From the first the crossed seedlings appeared the finest, and when they were on an average, by estimation, 5 inches high, the self-fertilised
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CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
The seeds just alluded to were allowed to germinate on bare sand, and were planted in pairs on the opposite sides of four pots. When the seedlings were in full flower, the tallest stem on each plant was measured to the base of the calyx. The measurements are given in Table 4/46. In Pot 1 the crossed and self-fertilised plants flowered at the same time; but in the other three pots the crossed flowered first. These latter plants also continued flowering much later in the autumn than the self-ferti
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THE EFFECTS OF A CROSS WITH A FRESH STOCK.
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
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NUMBER OF CAPSULES:
NUMBER OF CAPSULES:
The London-crossed to the self-fertilised as 100 to 39. The London-crossed to the intercrossed as 100 to 45. The intercrossed to the self-fertilised as 100 to 67. The London-crossed to the self-fertilised as 100 to 33. The intercrossed to the self-fertilised as 100 to 73. We thus see how greatly the offspring from the self-fertilised plants of the third generation crossed by a fresh stock, had their fertility increased, whether tested by the number of capsules produced or by the weight of the co
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COLOUR OF THE FLOWERS.
COLOUR OF THE FLOWERS.
The flowers produced by the self-fertilised plants of the last or fourth generation were as uniform in tint as those of a wild species, being of a pale pink or rose colour. Analogous cases with Mimulus and Ipomoea, after several generations of self-fertilisation, have been already given. The flowers of the intercrossed plants of the fourth generation were likewise nearly uniform in colour. On the other hand, the flowers of the London-crossed plants, or those raised from a cross with the fresh st
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14. LEGUMINOSAE.
14. LEGUMINOSAE.
In this family I experimented on the following six genera, Lupinus, Phaseolus, Lathyrus, Pisum, Sarothamnus, and Ononis. [Lupinus luteus. (5/2. The structure of the flowers of this plant, and their manner of fertilisation, have been described by H. Muller ‘Befruchtung’ etc. page 243. The flowers do not secrete free nectar, and bees generally visit them for their pollen. Mr. Farrer, however, remarks ‘Nature’ 1872 page 499, that “there is a cavity at the back and base of the vexillum, in which I h
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
The spontaneously self-fertilised seeds just mentioned, and crossed seeds obtained by intercrossing the two crossed plants of the last generation, after germinating on sand, were planted in pairs on the opposite sides of three large pots. When the seedlings were only 4 inches in height, the crossed had a slight advantage over their opponents. When grown to their full height, every one of the crossed plants exceeded its opponent in height. Nevertheless the self-fertilised plants in all three pots
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
From crossed and self-fertilised seeds obtained in the manner just described, I succeeded in raising to maturity only a pair of plants, which were kept in a pot in the greenhouse. The crossed plant grew to a height of 33 inches, and the self-fertilised to that of 26 1/2 inches. The former produced, whilst still kept in the greenhouse, eight pods, containing on an average 2.77 seeds; and the latter only two pods, containing on an average 2.5 seeds. The average height of the two crossed plants of
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PLANTS OF THE SECOND GENERATION.
PLANTS OF THE SECOND GENERATION.
Many of the self-fertilised peas just referred to germinated on sand before any of the crossed ones, and were rejected. As soon as I got equal pairs, they were planted on the opposite sides of two large pots, which were kept in the greenhouse. The seedlings thus raised were the grandchildren of the Painted Lady, which was first crossed by the Purple variety. When the two lots were from 4 to 6 inches in height there was no difference between them. Nor was there any marked difference in the period
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A SUMMARY ON THE LEGUMINOSAE.
A SUMMARY ON THE LEGUMINOSAE.
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,
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VAR. SNOW-FLAKE.
VAR. SNOW-FLAKE.
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
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PLANTS OF THE SECOND GENERATION.
PLANTS OF THE SECOND GENERATION.
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 whi
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
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
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DINGY PURPLE VARIETY.
DINGY PURPLE VARIETY.
The flowers of this plant are so seldom visited during the day by insects in this country, that I have never seen an instance; but my gardener, on whom I can rely, once saw some humble-bees at work. Mr. Meehan says, that in the United States bees bore through the corolla for the nectar, and adds that their “fertilisation is carried on by night-moths.” (6/1. ‘Proceedings of the Academy of Natural Science of Philadelphia’ August 2, 1870 page 90.) In France M. Naudin, after castrating a large numbe
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
As in the last generation, many of the self-fertilised seeds germinated before the crossed. Seeds in an equal state of germination were planted on the opposite sides of three pots. The crossed seedlings soon greatly exceeded in height the self-fertilised. In Pot 1, when the tallest crossed plant was 10 1/2 inches high, the tallest self-fertilised was only 3 1/2 inches; in Pot 2 the excess in height of the crossed was not quite so great. The plants were treated as in the last generation, and when
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CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
TABLE 6/78. Petunia violacea (third generation; plants very young). Heights of plants measured in inches. Column 1: Number (Name) of Pot. Column 2: Crossed Plants. Column 3: Self-fertilised Plants. Pot 1 : 1 4/8 : 5 6/8. Pot 1 : 1 : 4 4/8. Pot 2 : 5 7/8 : 8 3/8. Pot 2 : 5 6/8 : 6 7/8. Pot 3 : 4 : 5 5/8. Pot 4 : 1 4/8 : 5 3/8. Total : 19.63 : 36.50. The above seeds were placed on sand, and after germinating were planted in pairs on the opposite sides of four pots; and all the remaining seeds were
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THE EFFECTS OF A CROSS WITH A FRESH STOCK.
THE EFFECTS OF A CROSS WITH A FRESH STOCK.
I procured from a garden in Westerham, whence my plants originally came, a fresh plant differing in no respect from mine except in the colour of the flowers, which was a fine purple. But this plant must have been exposed during at least four generations to very different conditions from those to which my plants had been subjected, as these had been grown in pots in the greenhouse. Eight flowers on the self-fertilised plants in Table 6/81, of the last or fourth self-fertilised generation, were fe
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RELATIVE FERTILITY OF THE THREE LOTS OF PLANTS.
RELATIVE FERTILITY OF THE THREE LOTS OF PLANTS.
None of the plants in pots in the greenhouse ever produced a capsule; and this may be attributed in chief part to the exclusion of moths. Therefore the fertility of the three lots could be judged of only by that of the plants growing out of doors, which from being left uncovered were probably cross-fertilised. The plants in the three rows were exactly of the same age and had been subjected to closely similar conditions, so that any difference in their fertility must be attributed to their differ
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COLOUR OF THE FLOWERS ON THE ABOVE THREE LOTS OF PLANTS.
COLOUR OF THE FLOWERS ON THE ABOVE THREE LOTS OF PLANTS.
The original mother-plant, from which the five successive self-fertilised generations were raised, bore dingy purple flowers. At no time was any selection practised, and the plants were subjected in each generation to extremely uniform conditions. The result was, as in some previous cases, that the flowers on all the self-fertilised plants, both in the pots and open ground, were absolutely uniform in tint; this being a dull, rather peculiar flesh colour. This uniformity was very striking in the
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CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
Twelve flowers on the crossed plants of the last generation growing in the four large pots just mentioned, were crossed with pollen from a crossed plant growing in one of the other pots; and twelve flowers on the self-fertilised plants were fertilised with their own pollen. All these flowers of both lots produced fine capsules. Ten of the crossed capsules contained by weight 38.92 grains of seeds, and ten of the self-fertilised capsules 37.74 grains; or as 100 to 97. Some of these seeds in an eq
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CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
CROSSED AND SELF-FERTILISED PLANTS OF THE THIRD GENERATION.
TABLE 6/86. Nicotiana tabacum (third generation). Seedlings from the self-fertilised plant A in pot 3, Table 6/85, of the last or second generation. Heights of plants measured in inches. Column 1: Number (Name) of Pot. Column 2: From Self-fertilised Plant, crossed by a Crossed Plant. Column 3: From Self-fertilised Plant again self-fertilised, forming the third Self-fertilised generation. Pot 1 : 100 2/8 : 98. Pot 1 : 91 : 79. Pot 2 : 110 2/8 : 59 1/8. Pot 2 : 100 4/8 : 66 6/8. Pot 3 : 104 : 79 6
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THE EFFECTS OF A CROSS WITH A FRESH STOCK.
THE EFFECTS OF A CROSS WITH A FRESH STOCK.
I procured some seed of N. tabacum from Kew and raised some plants, which formed a slightly different sub-variety from my former plants; as the flowers were a shade pinker, the leaves a little more pointed, and the plants not quite so tall. Therefore the advantage in height which the seedlings gained by this cross cannot be attributed to direct inheritance. Two of the plants of the third self-fertilised generation, growing in Pots 2 and 5 in Table 6/87, which exceeded in height their crossed opp
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175.63 : 101.50 : 202.75 : 105.13.
175.63 : 101.50 : 202.75 : 105.13.
The twelve tallest crossed plants in the two pots belonging to the two series average here 31.53, and the twelve tallest self-fertilised plants 17.21 inches in height; or as 100 to 54. The plants on both sides, when fully grown, some time after they had been measured, were cut down close to the ground and weighed. The twelve crossed plants weighed 21.25 ounces; and the twelve self-fertilised plants only 7.83 ounces; or in weight as 100 to 37. The rest of the crossed and self-fertilised seeds fro
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478.75 : 286.86 : 496.13 : 417.25
478.75 : 286.86 : 496.13 : 417.25
The twenty tallest crossed plants here average 48.74, and the twenty tallest self-fertilised 35.2 inches in height; or as 100 to 72. These plants after being measured were cut down close to the ground, and the twenty crossed plants weighed 195.75 ounces, and the twenty self-fertilised plants 123.25 ounces; or as 100 to 63. In Tables 6/88, 6/89 and 6/90, we have the measurements of fifty-six plants derived from two plants of the third self-fertilised generation crossed with pollen from a fresh st
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ANAGALLIS.
ANAGALLIS.
Anagallis collina, var. grandiflora (pale red and blue-flowered sub-varieties). Firstly, twenty-five flowers on some plants of the red variety were crossed with pollen from a distinct plant of the same variety, and produced ten capsules; thirty-one flowers were fertilised with their own pollen, and produced eighteen capsules. These plants, which were grown in pots in the greenhouse, were evidently in a very sterile condition, and the seeds in both sets of capsules, especially in the self-fertili
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THE COWSLIP.
THE COWSLIP.
Most of the species in this genus are heterostyled or dimorphic; that is, they present two forms,—one long-styled with short stamens, and the other short-styled with long stamens. (6/6. See my paper ‘On the Two Forms or Dimorphic Condition in the Species of Primula’ in ‘Journal of the Proceedings of the Linnean Society’ volume 6 1862 page 77. A second paper, to which I presently refer ‘On the Hybrid-like Nature of the Offspring from the Illegitimate Unions of Dimorphic and Trimorphic Plants’ was
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EQUAL-STYLED AND RED-FLOWERED VAR.
EQUAL-STYLED AND RED-FLOWERED VAR.
I have described in my paper ‘On the Illegitimate Unions of Dimorphic and Trimorphic Plants’ this remarkable variety, which was sent to me from Edinburgh by Mr. J. Scott. It possessed a pistil proper to the long-styled form, and stamens proper to the short-styled form; so that it had lost the heterostyled or dimorphic character common to most of the species of the genus, and may be compared with an hermaphrodite form of a bisexual animal. Consequently the pollen and stigma of the same flower are
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A SUMMARY OF THE MEASUREMENTS IN TABLE 7/C.
A SUMMARY OF THE MEASUREMENTS IN TABLE 7/C.
This table includes the heights and often the weights of 292 plants derived from a cross with a fresh stock, and of 305 plants, either of self-fertilised origin, or derived from an intercross between plants of the same stock. These 597 plants belong to thirteen species and twelve genera. The various precautions which were taken to ensure a fair comparison have already been stated. If we now look down the right hand column, in which the mean height, weight, and fertility of the plants derived fro
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TABLE 7/A.
TABLE 7/A.
We will now turn to our first table, which relates to crossed and self-fertilised plants of the same stock. These consist of fifty-four species belonging to thirty natural orders. The total number of crossed plants of which measurements are given is 796, and of self-fertilised 809; that is altogether 1,605 plants. Some of the species were experimented on during several successive generations; and it should be borne in mind that in such cases the crossed plants in each generation were crossed wit
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TABLE 7/B.
TABLE 7/B.
A few words must be added on the weights of the crossed plants of the same stock, in comparison with the self-fertilised. Eleven cases are given in Table 7/B, relating to eight species. The number of plants which were weighed is shown in the two left columns, and their relative weights in the right column, that of the crossed plants being taken as 100. A few other cases have already been recorded in Table 7/C in reference to plants crossed by a fresh stock. I regret that more trials of this kind
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GREATER CONSTITUTIONAL VIGOUR OF CROSSED PLANTS.
GREATER CONSTITUTIONAL VIGOUR OF CROSSED PLANTS.
As in almost all my experiments an equal number of crossed and self-fertilised seeds, or more commonly seedlings just beginning to sprout, were planted on the opposite sides of the same pots, they had to compete with one another; and the greater height, weight, and fertility of the crossed plants may be attributed to their possessing greater innate constitutional vigour. Generally the plants of the two lots whilst very young were of equal height; but afterwards the crossed gained insensibly on t
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PERIOD OF FLOWERING.
PERIOD OF FLOWERING.
In some cases, as with Digitalis, Dianthus, and Reseda, a larger number of the crossed than of the self-fertilised plants threw up flower-stems; but this probably was merely the result of their greater power of growth; for in the first generation of Lobelia fulgens, in which the self-fertilised plants greatly exceeded in height the crossed plants, some of the latter failed to throw up flower-stems. With a large number of species, the crossed plants exhibited a well-marked tendency to flower befo
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EFFECTS OF CROSSING FLOWERS ON THE SAME PLANT.
EFFECTS OF CROSSING FLOWERS ON THE SAME PLANT.
In the discussion on the results of a cross with a fresh stock, given under Table 7/C in the last chapter, it was shown that the mere act of crossing by itself does no good; but that the advantages thus derived depend on the plants which are crossed, either consisting of distinct varieties which will almost certainly differ somewhat in constitution, or on the progenitors of the plants which are crossed, though identical in every external character, having been subjected to somewhat different con
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SELF-STERILE PLANTS.
SELF-STERILE PLANTS.
The cases here to be described might have been introduced in Table 9/F, which gives the relative fertility of flowers fertilised with their own pollen, and with that from a distinct plant, but it has been found more convenient to keep them for separate discussion. The present cases must not be confounded with those to be given in the next chapter relatively to flowers which are sterile when insects are excluded; for such sterility depends not merely on the flowers being incapable of fertilisatio
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CONCLUDING REMARKS ON SELF-STERILE PLANTS.
CONCLUDING REMARKS ON SELF-STERILE PLANTS.
In order to favour as far as possible the self-fertilisation of some of the foregoing plants, all the flowers on Reseda odorata and some of those on the Abutilon were fertilised with pollen from other flowers on the same plant, instead of with their own pollen, and in the case of the Senecio with pollen from other flowers on the same corymb; but this made no difference in the result. Fritz Muller tried both kinds of self-fertilisation in the case of Bignonia, Tabernaemontana and Abutilon, likewi
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THE APPEARANCE OF HIGHLY SELF-FERTILE VARIETIES.
THE APPEARANCE OF HIGHLY SELF-FERTILE VARIETIES.
We have just seen that the degree to which flowers are capable of being fertilised with their own pollen differs much, both with the species of the same genus, and sometimes with the individuals of the same species. Some allied cases of the appearance of varieties which, when self-fertilised, yield more seed and produce offspring growing taller than their self-fertilised parents, or than the intercrossed plants of the corresponding generation, will now be considered. Firstly, in the third and fo
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MEANS OF CROSS-FERTILISATION.
MEANS OF CROSS-FERTILISATION.
The most important of all the means by which pollen is carried from the anthers to the stigma of the same flower, or from flower to flower, are insects, belonging to the orders of Hymenoptera, Lepidoptera, and Diptera; and in some parts of the world, birds. (10/1. I will here give all the cases known to me of birds fertilising flowers. In South Brazil, humming-birds certainly fertilise the various species of Abutilon, which are sterile without their aid (Fritz Muller ‘Jenaische Zeitschrift f. Na
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ANEMOPHILOUS PLANTS.
ANEMOPHILOUS PLANTS.
The nature and relations of plants which are fertilised by the wind have been admirably discussed by Delpino and Hermann Muller; and I have already made some remarks on the structure of their flowers in contrast with those of entomophilous species. (10/42. Delpino ‘Ult. Osservazioni sulla Dicogamia’ part 2 fasc. 1 1870 and ‘Studi sopra un Lignaggio anemofilo’ etc. 1871. Hermann Muller ‘Die Befruchtung’ etc. pages 412, 442. Both these authors remark that plants must have been anemophilous before
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PERFORATION OF THE COROLLA BY BEES.
PERFORATION OF THE COROLLA BY BEES.
I have already alluded to bees biting holes in flowers for the sake of obtaining the nectar. They often act in this manner, both with endemic and exotic species, in many parts of Europe, in the United States, and in the Himalaya; and therefore probably in all parts of the world. The plants, the fertilisation of which actually depends on insects entering the flowers, will fail to produce seed when their nectar is stolen from the outside; and even with those species which are capable of fertilisin
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