The Different Forms Of Flowers On Plants Of The Same Species - free ebook by Charles Darwin

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The Different Forms Of Flowers On Plants Of The Same Species

Charles Darwin

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TO PROFESSOR ASA GRAY THIS VOLUME IS DEDICATED BY THE AUTHOR AS A SMALL TRIBUTE OF RESPECT AND AFFECTION.

TO PROFESSOR ASA GRAY THIS VOLUME IS DEDICATED BY THE AUTHOR AS A SMALL TRIBUTE OF RESPECT AND AFFECTION.

CONTENTS DETAILED TABLE OF CONTENTS THE DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES. INTRODUCTION. CHAPTER I. HETEROSTYLED DIMORPHIC PLANTS: PRIMULACEÆ. CHAPTER II. HYBRID PRIMULAS. CHAPTER III. HETEROSTYLED DIMORPHIC PLANTS—continued. CHAPTER IV. HETEROSTYLED TRIMORPHIC PLANTS. CHAPTER V. ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS. CONCLUSIONS WITH RESPECT TO THE EQUAL-STYLED VARIETY OF P. Sinensis. CHAPTER VI. CONCLUDING REMARKS ON HETEROSTYLED PLANTS. CHAPTER VII. POLYGAMOUS,

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INTRODUCTION.

INTRODUCTION.

The subject of the present volume, namely the differently formed flowers normally produced by certain kinds of plants, either on the same stock or on distinct stocks, ought to have been treated by a professed botanist, to which distinction I can lay no claim. As far as the sexual relations of flowers are concerned, Linnaeus long ago divided them into hermaphrodite, monoecious, dioecious, and polygamous species. This fundamental distinction, with the aid of several subdivisions in each of the fou

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TABLE 1.1.

TABLE 1.1.

Column 1: Plant. Column 2: Number of Plants. Column 3: Number of Umbels Produced. Column 4: Number of Capsules Produced. Column 5: Weight of Seed In Grains. Short-styled cowslips : 9 : 33 : 199 : 83. Long-styled cowslips : 13 : 51 : 261 : 91. If we compare the weight from an equal number of plants, and from an equal number of umbels, and from an equal number of capsules of the two forms, we get the following results:—...

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TABLE 1.2.

TABLE 1.2.

Column 1: Plant. Column 2: Number of Plants. Column 3: Weight of Seed in grains. ... Column 4: Number of Umbels. Column 5: Weight of Seed. ... Column 6: Number of Capsules. Column 7: Weight of Seed in grains. Short-styled cowslips : 10 : 92 :: 100 : 251 :: 100 : 41. Long-styled cowslips : 10 : 70 :: 100 : 178 :: 100 : 34. So that, by all these standards of comparison, the short-styled form is the more fertile; if we take the number of umbels (which is the fairest standard, for large and small pl

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TABLE 1.3.

TABLE 1.3.

Column 1: Plant. Column 2: Number of Plants. Column 3: Number of Umbels. Column 4: Weight of Seed in grains. Short-styled cowslips : 47 : 173 : 745. Long-styled cowslips : 58 : 208 : 692. These figures give us the following proportions:—...

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TABLE 1.4.

TABLE 1.4.

Column 1: Plant. Column 2: Number of Plants. Column 3: Weight of Seed in grains. ... Column 4: Number of Umbels. Column 5: Weight of Seed in grains. Short-styled cowslips : 100 : 1585 :: 100 : 430. Long-styled cowslips : 100 : 1093 :: 100 : 332. The season was much more favourable this year than the last; the plants also now grew in good soil, instead of in a shady wood or struggling with other plants in the open field; consequently the actual produce of seed was considerably larger. Nevertheles

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TABLE 1.5.

TABLE 1.5.

Column 1: Plant. Column 2: Number of Plants. Column 3: Number of Umbels produced. Column 4: Product of Seed. Short-styled : 6 : 24 : 1.3 grain weight of seed, or about 50 in number. Long-styled : 18 : 74 : Not one seed. Judging from the exposed plants which grew all round in the same bed, and had been treated in the same manner, excepting that they had been exposed to the visits of insects, the above six short-styled plants ought to have produced 92 grains’ weight of seed instead of only 1.3; an

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A SUMMARY:

A SUMMARY:

The two legitimate unions : 35 : 27 : 25 : 13.7 : 54. The two illegitimate unions : 35 : 16 : 11 : 3.9 : 35. The results may be given in another form (Table 1.7) by comparing, first, the number of capsules, whether good or bad, or of the good alone, produced by 100 flowers of both forms when legitimately and illegitimately fertilised; secondly, by comparing the weight of seed in 100 of these capsules, whether good or bad; or, thirdly, in 100 of the good capsules. TABLE 1.7. Primula veris. Column

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A SUMMARY:

A SUMMARY:

The two legitimate unions together : 20 : 14 : 62 : 37 : 47.1. The two illegitimate unions together : 37 : 7 : 49* : 2 : 35.5. (*These seeds were so poor and small that they could hardly have germinated.) If we compare the fertility of the two legitimate unions taken together with that of the two illegitimate unions together, as judged by the proportional number of flowers which when fertilised in the two methods yielded capsules, the ratio is as 100 to 27; so that by this standard the present s

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A SUMMARY:

A SUMMARY:

The two legitimate unions together : 20 : 18 : 77 : 47 : 66.0. The two illegitimate unions together : 39 : 21 : 66 : 5 : 35.5 (This average is perhaps rather too low). We may infer from this table that the fertility of the two legitimate unions taken together is to that of the two illegitimate unions together, as judged by the proportional number of flowers which when fertilised in the two methods yielded capsules, as 100 to 60. If we judge by the average number of seeds per capsule produced by

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A SUMMARY:

A SUMMARY:

The two legitimate unions together : 32 : 24 : 0.64 :: 57. The two illegitimate unions together : 27 : 17 : 0.40 :: 30. The fertility, therefore, of the two legitimate unions together to that of the two illegitimate unions, as judged by the proportional number of flowers which yielded capsules, is as 100 to 84. Judging by the average weight of seeds per capsule produced by the two kinds of unions, the ratio is as 100 to 63. On another occasion a large number of flowers of both forms were fertili

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A SUMMARY:

A SUMMARY:

The two legitimate unions together : 28 : 28 : 43. The two illegitimate unions together (own-form pollen): 42 : 42 : 18. The two illegitimate unions together (pollen from the same flower ): 48 : 32 : 13. Hildebrand in the paper above referred to gives the results of his experiments on the present species; and these are shown in a condensed form in Table 1.11. Besides using for the illegitimate unions pollen from a distinct plant of the same form, as was always done by me, he tried, in addition,

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A SUMMARY ON THE FOREGOING HETEROSTYLED SPECIES OF PRIMULA.

A SUMMARY ON THE FOREGOING HETEROSTYLED SPECIES OF PRIMULA.

TABLE 1.12. Summary on the Fertility of the two Legitimate Unions, compared with that of the two Illegitimate Unions, in the genus Primula. The former taken at 100. Column 1: Name of Species. Column 2: Illegitimate Unions, Judged of by the Proportional Number of Flowers which produced Capsules. Column 3: Illegitimate Unions, Judged of by the Average Number (or Weight in some cases) of Seeds per Capsule. Primula veris : 69 : 65. Primula elatior : 27 : 75 (Probably too high). Primula vulgaris : 60

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HOMOSTYLED SPECIES OF PRIMULA.

HOMOSTYLED SPECIES OF PRIMULA.

It has now been shown that nine of the species in this genus exist under two forms, which differ not only in structure but in function. Besides these Mr. Scott enumerates 27 other species which are heterostyled (1/13. H. Muller has given in ‘Nature’ December 10, 1874 page 110, a drawing of one of these species, viz. The alpine P. villosa, and shows that it is fertilised exclusively by Lepidoptera.); and to these probably others will be hereafter added. Nevertheless, some species are homostyled;

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A SUMMARY:

A SUMMARY:

The two legitimate unions together: 64 : 78.8. The two illegitimate unions together: 37 : 48.1. The most remarkable point in this table is the small average number of seeds from the short-styled flowers when illegitimately fertilised, and the unusually large average number of seeds yielded by the illegitimately fertilised long- styled flowers, relatively in both cases to the product of the legitimately fertilised flowers. (1/18. H. Muller says ‘Die Befruchtung’ etc. page 352, that the long-style

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SUPPLEMENTARY NOTE ON SOME WILD HYBRID VERBASCUMS.

SUPPLEMENTARY NOTE ON SOME WILD HYBRID VERBASCUMS.

In an early part of this chapter I remarked that few other instances could be given of a hybrid spontaneously arising in such large numbers, and over so wide an extent of country, as that of the common oxlip; but perhaps the number of well-ascertained cases of naturally produced hybrid willows is equally great. (2/19. Max Wichura ‘Die Bastardbefruchtung etc. der Weiden’ 1865.) Numerous spontaneous hybrids between several species of Cistus, found near Narbonne, have been carefully described by M.

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FIRST.

FIRST.

Pollen from a short-styled plant was placed on the five stigmas of a long-styled flower, and these, after thirty hours, were found deeply penetrated by a multitude of pollen-tubes, far too numerous to be counted; the stigmas had also become discoloured and twisted. I repeated this experiment on another flower, and in eighteen hours the stigmas were penetrated by a multitude of long pollen- tubes. This is what might have been expected, as the union is a legitimate one. The converse experiment was

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SECONDLY.

SECONDLY.

Pollen from a long-styled flower was placed on all five stigmas of a long-styled flower on a separate plant: after nineteen hours the stigmas were dissected, and only a single pollen-grain had emitted a tube, and this was a very short one. To make sure that the pollen was good, I took in this case, and in most of the other cases, pollen either from the same anther or from the same flower, and proved it to be good by placing it on the stigma of a short-styled plant, and found numerous pollen-tube

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THIRDLY.

THIRDLY.

Repeated last experiment, and placed own-form pollen on all five stigmas of a long-styled flower; after nineteen hours and a half, not one single grain had emitted its tube....

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FOURTHLY.

FOURTHLY.

Repeated the experiment, with the same result after twenty-four hours....

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FIFTHLY.

FIFTHLY.

Repeated last experiment, and, after leaving pollen on for nineteen hours, put on an additional quantity of own-form pollen on all five stigmas. After an interval of three days, the stigmas were examined, and, instead of being discoloured and twisted, they were straight and fresh-coloured. Only one grain had emitted a quite short tube, which was drawn out of the stigmatic tissue without being ruptured. The following experiments are more striking:—...

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SIXTHLY.

SIXTHLY.

I placed own-form pollen on three of the stigmas of a long-styled flower, and pollen from a short-styled flower on the other two stigmas. After twenty-two hours these two stigmas were discoloured, slightly twisted, and penetrated by the tubes of numerous pollen-grains: the other three stigmas, covered with their own-form pollen, were fresh, and all the pollen-grains were loose; but I did not dissect the whole stigma....

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SEVENTHLY.

SEVENTHLY.

Experiment repeated in the same manner, with the same result....

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EIGHTHLY.

EIGHTHLY.

Experiment repeated, but the stigmas were carefully examined after an interval of only five hours and a half. The two stigmas with pollen from a short-styled flower were penetrated by innumerable tubes, which were as yet short, and the stigmas themselves were not at all discoloured. The three stigmas covered with their own-form pollen were not penetrated by a single pollen-tube....

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NINTHLY.

NINTHLY.

Put pollen of a short-styled flower on a single long-styled stigma, and own-form pollen on the other four stigmas; after twenty-four hours the one stigma was somewhat discoloured and twisted, and penetrated by many long tubes: the other four stigmas were quite straight and fresh; but on dissecting them I found that three pollen-grains had protruded very short tubes into the tissue....

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TENTHLY.

TENTHLY.

Repeated the experiment, with the same result after twenty-four hours, excepting that only two own-form grains had penetrated the stigmatic tissue with their tubes to a very short depth. The one stigma, which was deeply penetrated by a multitude of tubes from the short-styled pollen, presented a conspicuous difference in being much curled, half-shrivelled, and discoloured, in comparison with the other four straight and bright pink stigmas. I could add other experiments; but those now given amply

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PULMONARIA (BORAGINEAE).

PULMONARIA (BORAGINEAE).

Pulmonaria officinalis. Hildebrand has published a full account of this heterostyled plant. (3/11. ‘Botanische Zeitung’ 1865 January 13 page 13.) The pistil of the long-styled form is twice as long as that of the short-styled; and the stamens differ in a corresponding, though converse, manner. There is no marked difference in the shape or state of surface of the stigma in the two forms. The pollen-grains of the short-styled form are to those of the long-styled as 9 to 7, or as 100 to 78, in leng

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RUBIACEAE.

RUBIACEAE.

This great natural family contains a much larger number of heterostyled genera than any other one, as yet known. Mitchella repens. Professor Asa Gray sent me several living plants collected when out of flower, and nearly half of these proved long-styled, and the other half short-styled. The white flowers, which are fragrant and which secrete plenty of nectar, always grow in pairs with their ovaries united, so that the two together produce “a berry-like double drupe.” (3/22. A. Gray ‘Manual of th

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LONG-STYLED FORM.

LONG-STYLED FORM.

This form can be at once recognised by the length of the pistil, which is (including the ovarium) fully one-third longer than that of the mid-styled, and more than thrice as long as that of the short-styled form. It is so disproportionately long, that it projects in the bud through the folded petals. It stands out considerably beyond the mid-length stamens; its terminal portion depends a little, but the stigma itself is slightly upturned. The globular stigma is considerably larger than that of t

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MID-STYLED FORM.

MID-STYLED FORM.

The pistil occupies the position represented in Figure 4.10, with its extremity considerably upturned, but to a variable degree; the stigma is seated between the anthers of the longest and the shortest stamens. The six longest stamens correspond in length with the pistil of the long-styled form; their filaments are coloured bright pink; the anthers are dark-coloured, but from containing bright-green pollen and from their early dehiscence they appear emerald-green. Hence in general appearance the

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SHORT-STYLED FORM.

SHORT-STYLED FORM.

The pistil is here very short, not one-third of the length of that of the long- styled form. It is enclosed within the calyx, which, differently from that in the other two forms, does not enclose any anthers. The end of the pistil is generally bent upwards at right angles. The six longest stamens, with their pink filaments and green pollen, resemble the corresponding stamens of the mid-styled form. But according to H. Muller, their pollen-grains are a little larger, namely 9 1/2 to 10 1/2, inste

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ON THE POWER OF MUTUAL FERTILISATION BETWEEN THE THREE FORMS.

ON THE POWER OF MUTUAL FERTILISATION BETWEEN THE THREE FORMS.

Nothing shows more clearly the extraordinary complexity of the reproductive system of this plant, than the necessity of making eighteen distinct unions in order to ascertain the relative fertilising power of the three forms. Thus the long-styled form has to be fertilised with pollen from its own two kinds of anthers, from the two in the mid-styled, and from the two in the short-styled form. The same process has to be repeated with the mid-styled and short-styled forms. It might have been thought

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A SUMMARY OF THE RESULTS. LONG-STYLED FORM.

A SUMMARY OF THE RESULTS. LONG-STYLED FORM.

Twenty-six flowers fertilised legitimately by the stamens of corresponding length, borne by the mid-and short-styled forms, yielded 61.5 per cent of capsules, which contained on an average 89.7 seeds. Twenty-six long-styled flowers fertilised illegitimately by the other stamens of the mid-and short-styled forms yielded only two very poor capsules. Thirty long-styled flowers fertilised illegitimately by their own-form two sets of stamens yielded only eight very poor capsules; but long-styled flow

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MID-STYLED FORM.

MID-STYLED FORM.

Twenty-four flowers legitimately fertilised by the stamens of corresponding length, borne by the long and short-styled forms, yielded 96 (probably 100) per cent of capsules, which contained (excluding one capsule with 12 seeds) on an average 117.2 seeds. Fifteen mid-styled flowers fertilised illegitimately by the longest stamens of the short-styled form yielded 93 per cent of capsules, which (excluding four capsules with less than 20 seeds) contained on an average 102.8 seeds. Thirteen mid-style

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SHORT-STYLED FORM.

SHORT-STYLED FORM.

Twenty-five flowers fertilised legitimately by the stamens of corresponding length, borne by the long and mid-styled forms, yielded 72 per cent of capsules, which (excluding one capsule with only 9 seeds) contained on an average 70.8 seeds. Twenty short-styled flowers fertilised illegitimately by the other stamens of the long and mid-styled forms yielded only two very poor capsules. Twenty short-styled flowers fertilised illegitimately by their own stamens yielded only two poor (or perhaps three

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TABLE 4.26.

TABLE 4.26.

Column 1: Nature of union. Column 2: Number of Flowers fertilised. Column 3: Number of Capsules produced. Column 4: Average Number of Seeds per Capsule. Column 5: Average Number of Seeds per Flower fertilised. The six legitimate unions : 75 : 56 : 96.29 : 71.89. The twelve illegitimate unions : 146 : 36 : 44.72 : 11.03. Therefore the fertility of the legitimate unions to that of the illegitimate, as judged by the proportion of the fertilised flowers which yielded capsules, is as 100 to 33; and j

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HOMOSTYLED SPECIES OF OXALIS.

HOMOSTYLED SPECIES OF OXALIS.

Although the majority of the species in the large genus Oxalis seem to be trimorphic, some are homostyled, that is, exist under a single form; for instance the common O. acetosella, and according to Hildebrand two other widely distributed European species, O. stricta and corniculata. Fritz Muller also informs me that a similarly constituted species is found in St. Catharina, and that it is quite fertile with its own pollen when insects are excluded. The stigmas of O. stricta and of another homos

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PONTEDERIA [SP.?] (PONTEDERIACEAE).

PONTEDERIA [SP.?] (PONTEDERIACEAE).

Fritz Muller found this aquatic plant, which is allied to the Liliaceae, growing in the greatest profusion on the banks of a river in Southern Brazil. (4/15. “Ueber den Trimorphismus der Pontederien” ‘Jenaische Zeitschrift’ etc. Band 6 1871 page 74.) But only two forms were found, the flowers of which include three long and three short stamens. The pistil of the long-styled form, in two dried flowers which were sent me, was in length as 100 to 32, and its stigma as 100 to 80, compared with the s

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[PLANT 1.

[PLANT 1.

This long-styled plant was allowed during 1863 to be freely and legitimately fertilised by an adjoining illegitimate mid-styled plant, but it did not yield a single seed-capsule. It was then removed and planted in a remote place close to a brother long-styled plant Number 2, so that it must have been freely though illegitimately fertilised; under these circumstances it did not yield during 1864 and 1865 a single capsule. I should here state that a legitimate or ordinary long-styled plant, when g

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PLANT 2.

PLANT 2.

This long-styled plant, after flowering during 1863 close to an illegitimate mid-styled plant, produced less than twenty capsules, which contained on an average between four and five seeds. When subsequently growing in company with Number 1, by which it will have been illegitimately fertilised, it yielded in 1866 not a single capsule, but in 1865 it yielded twenty-two capsules: the best of these, fifteen in number, were examined; eight contained no seed, and the remaining seven contained on an a

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PLANTS 3 AND 4.

PLANTS 3 AND 4.

These two long-styled plants, after being freely and legitimately fertilised during 1863 by the same illegitimate mid-styled plant as in the last case, were as miserably sterile as Number 2....

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PLANT 5.

PLANT 5.

This long-styled plant, after flowering in 1863 close to an illegitimate mid- styled plant, yielded only four capsules, which altogether included only five seeds. During 1864, 1865, and 1866, it was surrounded either by illegitimate or legitimate plants of the other two forms; but it did not yield a single capsule. It was a superfluous experiment, but I likewise artificially fertilised in a legitimate manner twelve flowers; but not one of these produced a capsule; so that this plant was almost a

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PLANT 6.

PLANT 6.

This long-styled plant, after flowering during the favourable year of 1866, surrounded by illegitimate plants of the other two forms, did not produce a single capsule....

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PLANT 7.

PLANT 7.

This long-styled plant was the most fertile of the eight plants of the first lot. During 1865 it was surrounded by illegitimate plants of various parentage, many of which were highly fertile, and must thus have been legitimately fertilised. It produced a good many capsules, ten of which yielded an average of 36.1 seeds, with a maximum of 47 and a minimum of 22; so that this plant produced 39 per cent of the full number of seeds. During 1864 it was surrounded by legitimate and illegitimate plants

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[PLANT 8.

[PLANT 8.

This plant was allowed to be freely fertilised in 1864 by legitimate and illegitimate plants of the other two forms, and ten capsules yielded on an average 41.1 seeds, with a maximum of 73 and a minimum of 11. Hence this plant produced only 44 per cent of the full complement of seeds....

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PLANT 9.

PLANT 9.

This long-styled plant was allowed in 1865 to be freely fertilised by illegitimate plants of the other two forms, most of which were moderately fertile. Fifteen capsules yielded on an average 57.1 seeds, with a maximum of 86 and a minimum of 23. Hence the plant yielded 61 per cent of the full complement of seeds....

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PLANT 10.

PLANT 10.

This long-styled plant was freely fertilised at the same time and in the same manner as the last. Ten capsules yielded an average of 44.2 seeds, with a maximum of 69 and a minimum of 25; hence this plant yielded 47 per cent of the full complement of seeds.] The nineteen long-styled plants of the third lot, of the same parentage as the last lot, were treated differently; for they flowered during 1867 by themselves so that they must have been illegitimately fertilised by one another. It has alread

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[PLANT 11.

[PLANT 11.

This long-styled plant produced a large crop of capsules, and in this respect was one of the most fertile of the whole lot of nineteen plants. But the average from ten capsules was only 35.9 seeds, with a maximum of 60 and a minimum of 8....

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PLANT 12.

PLANT 12.

This long-styled plant produced very few capsules; and ten yielded an average of only 15.4 seeds, with a maximum of 30 and a minimum of 4....

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PLANT 13.

PLANT 13.

This plant offers an anomalous case; it flowered profusely, yet produced very few capsules; but these contained numerous seeds. Ten capsules yielded an average of 71.9 seeds, with a maximum of 95 and a minimum of 29. Considering that this plant was illegitimate and illegitimately fertilised by its brother long-styled seedlings, the average and the maximum are so remarkably high that I cannot at all understand the case. We should remember that the average for a legitimate plant legitimately ferti

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[PLANT 14.

[PLANT 14.

This short-styled plant was allowed during 1865 to be freely and legitimately fertilised by illegitimate plants descended from self-fertilised mid-, long- and short-styled plants. Fifteen capsules yielded an average of 28.3 seeds, with a maximum of 51 and a minimum of 11; hence this plant produced only 33 per cent of the proper number of seeds. The seeds themselves were small and irregular in shape. Although so sterile on the female side, none of the anthers were contabescent....

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PLANT 15.

PLANT 15.

This short-styled plant, treated like the last during the same year, yielded an average, from fifteen capsules, of 27 seeds, with a maximum of 49 and a minimum of 7. But two poor capsules may be rejected, and then the average rises to 32.6, with the same maximum of 49 and a minimum of 20; so that this plant attained 38 per cent of the normal standard of fertility, and was rather more fertile than the last, yet many of the anthers were contabescent....

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PLANT 16.

PLANT 16.

This short-styled plant, treated like the two last, yielded from ten capsules an average of 77.8 seeds, with a maximum of 97 and a minimum of 60; so that this plant produced 94 per cent of the full number of seeds....

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PLANT 17.

PLANT 17.

This, the one long-styled plant of the same parentage as the last three plants, when freely and legitimately fertilised in the same manner as the last, yielded an average from ten capsules of 76.3 rather poor seeds, with a maximum of 88 and a minimum of 57. Hence this plant produced 82 per cent of the proper number of seeds. Twelve flowers enclosed in a net were artificially and legitimately fertilised with pollen from a legitimate short-styled plant; and nine capsules yielded an average of 82.5

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[PLANT 18.

[PLANT 18.

This mid-styled plant, when freely and legitimately fertilised during 1865 by illegitimate plants descended from self-fertilised long-, short-, and mid-styled plants, yielded an average from ten capsules of 102.6 seeds, with a maximum of 131 and a minimum of 63: hence this plant did not produce quite 80 per cent of the normal number of seeds. Twelve flowers were artificially and legitimately fertilised with pollen from a legitimate long-styled plant, and yielded from nine capsules an average of

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PLANT 19.

PLANT 19.

This mid-styled plant, fertilised in the same manner and at the same period as the last, yielded an average from ten capsules of 73.4 seeds, with a maximum of 87 and a minimum of 64: hence this plant produced only 56 per cent of the full number of seeds. Thirteen flowers were artificially and legitimately fertilised with pollen from a legitimate long-styled plant, and yielded ten capsules with an average of 95.6 seeds; so that the application of pollen from a legitimate plant added, as in the tw

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PLANT 20.

PLANT 20.

This long-styled plant, of the same parentage with the two last mid-styled plants, and freely fertilised in the same manner, yielded an average from ten capsules of 69.6 seeds, with a maximum of 83 and a minimum of 52: hence this plant produced 75 per cent of the full number of seeds.] CLASS 5. ILLEGITIMATE PLANTS RAISED FROM A SHORT-STYLED PARENT FERTILISED WITH POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM. In the four previous classes, plants raised from the three forms fertilise

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[PLANT 21.

[PLANT 21.

This short-styled plant, freely and legitimately fertilised during 1865 by illegitimate plants, descended from self-fertilised long-, mid- and short-styled parents, yielded an average from ten capsules of 43 seeds, with a maximum of 63 and a minimum of 26: hence this plant, which was the one with all its longer and many of its shorter stamens contabescent, produced only 52 per cent of the proper number of seeds....

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PLANT 22.

PLANT 22.

This short-styled plant produced perfectly sound pollen, as viewed under the microscope. During 1866 it was freely and legitimately fertilised by other illegitimate plants belonging to the present and the following class, both of which include many highly fertile plants. Under these circumstances it yielded from eight capsules an average of 100.5 seeds, with a maximum of 123 and a minimum of 86; so that it produced 121 per cent of seeds in comparison with the normal standard. During 1864 it was

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PLANT 23.

PLANT 23.

This short-styled plant produced perfectly sound pollen. During 1866 it was freely and legitimately fertilised by the other illegitimate plants specified under the last experiment, and eight capsules yielded an average of 113.5 seeds, with a maximum of 123 and a minimum of 93. Hence this plant exceeded the normal standard, producing no less than 136 per cent of seeds....

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PLANT 24.

PLANT 24.

This long-styled plant produced pollen which seemed under the microscope sound; but some of the grains did not swell when placed in water. During 1864 it was legitimately fertilised by legitimate and illegitimate plants in the same manner as Plant 22, but yielded an average, from ten capsules, of only 55 seeds, with a maximum of 88 and a minimum of 24, thus attaining 59 per cent of the normal fertility. This low degree of fertility, I presume, was owing to the unfavourable season; for during 186

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PLANT 25.

PLANT 25.

The pollen of this long-styled plant contained a moderate number of poor and shrivelled grains; and this is a surprising circumstance, as it yielded an extraordinary number of seeds. During 1866 it was freely and legitimately fertilised by illegitimate plants, as described under Number 22, and yielded an average, from eight capsules, of 122.5 seeds, with a maximum of 149 and a minimum of 84. Hence this plant exceeded the normal standard, producing no less than 131 per cent of seeds.] CLASS 6. IL

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[PLANT 26.

[PLANT 26.

This mid-styled plant was freely and legitimately fertilised, during the rather unfavourable year 1864, by numerous surrounding legitimate and illegitimate plants. It yielded an average, from ten capsules, of 83.5 seeds, with a maximum of 110 and a minimum of 64, thus attaining 64 per cent of the normal fertility. During the highly favourable year 1866, it was freely and legitimately fertilised by illegitimate plants belonging to the present Class and to Class 5, and yielded an average, from eig

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PLANT 27.

PLANT 27.

This mid-styled plant, fertilised during 1864 in the same manner as the last, yielded an average, from ten capsules, of 99.4 seeds, with a maximum of 122 and a minimum of 53, thus attaining to 76 per cent of the normal fertility. If the season had been more favourable, its fertility would probably have been somewhat greater, but, judging from the last experiment, only in a slight degree....

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PLANT 28.

PLANT 28.

This mid-styled plant, when legitimately fertilised during the favourable season of 1866, in the manner described under Number 26, yielded an average, from eight capsules, of 89 seeds, with a maximum of 119 and a minimum of 69, thus producing 68 per cent of the full number of seeds. In the pollen of both sets of anthers, nearly as many grains were small and shrivelled as sound....

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PLANT 29.

PLANT 29.

This long-styled plant was legitimately fertilised during the unfavourable season of 1864, in the manner described under Number 26, and yielded an average, from ten capsules, of 84.6 seeds, with a maximum of 132 and a minimum of 47, thus attaining to 91 per cent of the normal fertility. During the highly favourable season of 1866, when fertilised in the manner described under Number 26, it yielded an average, from nine capsules (one poor capsule having been excluded), of 100 seeds, with a maximu

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[PLANT 32.

[PLANT 32.

This mid-styled plant was freely and legitimately fertilised during the unfavourable year of 1864, by numerous surrounding legitimate and illegitimate plants. Eight capsules yielded an average of 127.2 seeds, with a maximum of 144 and a minimum of 96; so that this plant attained 98 per cent of the normal standard....

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PLANT 33.

PLANT 33.

This short-styled plant was fertilised in the same manner and at the same time with the last; and ten capsules yielded an average of 113.9, with a maximum of 137 and a minimum of 90. Hence this plant produced no less than 137 per cent of seeds in comparison with the normal standard.] CONCLUDING REMARKS ON THE ILLEGITIMATE OFFSPRING OF THE THREE FORMS OF Lythrum salicaria. From the three forms occurring in approximately equal numbers in a state of nature, and from the results of sowing seed natur

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OXALIS.

OXALIS.

No one has compared the legitimate and illegitimate offspring of any trimorphic species in this genus. Hildebrand sowed illegitimately fertilised seeds of Oxalis Valdiviana, but they did not germinate (5/4. ‘Botanische Zeitung’ 1871 page 433 footnote.); and this fact, as he remarks, supports my view that an illegitimate union resembles a hybrid one between two distinct species, for the seeds in this latter case are often incapable of germination. [The following observations relate to the nature

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PRIMULA.

PRIMULA.

Primula Sinensis. I raised during February 1862, from some long-styled plants illegitimately fertilised with pollen from the same form, twenty-seven seedlings. These were all long-styled. They proved fully fertile or even fertile in excess; for ten flowers, fertilised with pollen from other plants of the same lot, yielded nine capsules, containing on an average 39.75 seeds, with a maximum in one capsule of 66 seeds. Four other flowers legitimately crossed with pollen from a legitimate plant, and

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VAR. RUBRA.

VAR. RUBRA.

Mr. Scott states that this variety, which grew in the Botanic Garden in Edinburgh, was quite sterile when fertilised with pollen from the common primrose, as well as from a white variety of the same species, but that some of the plants, when artificially fertilised with their own pollen, yielded a moderate supply of seed. (5/10. ‘Journal of the Proceedings of the Linnean Society’ 8 1864 page 98.) He was so kind as to send me some of these self- fertilised seeds, from which I raised the plants im

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PULMONARIA.

PULMONARIA.

I have little to say on this genus. I obtained seeds of P. officinalis from a garden where the long-styled form alone grew, and raised 11 seedlings, which were all long-styled. These plants were named for me by Dr. Hooker. They differed, as has been shown, from the plants belonging to this species which in Germany were experimented on by Hildebrand (5/13. ‘Botanische Zeitung’ 1865 page 13.); for he found that the long-styled form was absolutely sterile with its own pollen, whilst my long-styled

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DIMORPHIC SPECIES.

DIMORPHIC SPECIES.

Column 1: Name of species. Column 2: From the long-styled form : relative diameter. Primula veris : 67. Primula vulgaris : 71. Primula Sinensis (Hildebrand) : 57. Primula auricula : 71. Hottonia palustris (H. Muller) : 61. Hottonia palustris (self) : 64. Linum grandiflorum : 100. Linum perenne (diameter variable) : 100 (?). Linum flavum : 100. Pulmonaria officinalis : 78. Pulmonaria angustifolia : 91. Polygonum fagopyrum : 82. Leucosmia Burnettiana : 99. Aegiphila elata : 62. Menyanthes trifolia

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TRIMORPHIC SPECIES.

TRIMORPHIC SPECIES.

Column 1: Name of species. Column 2: Ratio expressing the extreme differences in diameter of the pollen- grains from the two sets of anthers in the three forms. Lythrum salicaria : 60. Nesaea verticillata : 65. Oxalis Valdiviana (Hildebrand) : 71. Oxalis Regnelli : 78. Oxalis speciosa : 69. Oxalis sensitiva : 84. Pontederia (sp.?) : 55. Column 1: Name of species. Column 2: Ratio between the diameters of the pollen-grains of the two sets of anthers in the same form. Oxalis rosea, long-styled form

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DICOTYLEDONS.

DICOTYLEDONS.

HYPERICINEAE: Cratoxylon. ERYTHROXYLEAE: Erythroxylum. Sethia. GERANIACEAE: Linum. Oxalis. LYTHRACEAE: Lythrum. Neseae. RUBIACEAE: Cinchona. Bouvardia. Manettia. Hedyotis. Oldenlandia. Houstonia. Coccocypselum. Lipostoma. Knoxia. Faramea. Psychotria. Rudgea. Suteria. Mitchella. Diodia. Borreria. Spermacoce. PRIMULACEAE: Primula. Hottonia. Androsace. OLEACEAE: Forsythia. GENTIANACEAE: Menyanthes. Limnanthemum. Villarsia. POLEMONIACEAE: Gilia. CORDIEAE: Cordia. BORAGINEAE: Pulmonaria. VERBENACEAE:

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MONOCOTYLEDONS.

MONOCOTYLEDONS.

PONTEDERIACEAE: Pontederia. In some of these families the heterostyled condition must have been acquired at a very remote period. Thus the three closely allied genera, Menyanthes, Limnanthemum, and Villarsia, inhabit respectively Europe, India, and South America. Heterostyled species of Hedyotis are found in the temperate regions of North and the tropical regions of South America. Trimorphic species of Oxalis live on both sides of the Cordillera in South America and at the Cape of Good Hope. In

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THE MEANS BY WHICH PLANTS MAY HAVE BEEN RENDERED HETEROSTYLED.

THE MEANS BY WHICH PLANTS MAY HAVE BEEN RENDERED HETEROSTYLED.

This is a very obscure subject, on which I can throw little light, but which is worthy of discussion. It has been shown that heterostyled plants occur in fourteen natural families, dispersed throughout the whole vegetable kingdom, and that even within the family of the Rubiaceae they are dispersed in eight of the tribes. We may therefore conclude that this structure has been acquired by various plants independently of inheritance from a common progenitor, and that it can be acquired without any

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TRANSMISSION OF THE TWO FORMS BY HETEROSTYLED PLANTS.

TRANSMISSION OF THE TWO FORMS BY HETEROSTYLED PLANTS.

The transmission of the two forms by heterostyled plants, with respect to which many facts were given in the last chapter, may perhaps be found hereafter to throw some light on their manner of development. Hildebrand observed that seedlings from the long-styled form of Primula Sinensis when fertilised with pollen from the same form were mostly long-styled, and many analogous cases have since been observed by me. All the known cases are given in Tables 6.36 and 6.37. TABLE 6.36. Nature of the off

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EQUAL-STYLED VARIETIES.

EQUAL-STYLED VARIETIES.

The tendency of the dimorphic species of Primula to produce equal-styled varieties deserves notice. Cases of this kind have been observed, as shown in the last chapter, in no less than six species, namely, P. veris, vulgaris, Sinensis, auricula, farinosa, and elatior. In the case of P. veris, the stamens resemble in length, position and size of their pollen-grains the stamens of the short-styled form; whilst the pistil closely resembles that of the long-styled, but as it varies much in length, o

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FINAL REMARKS.

FINAL REMARKS.

The existence of plants which have been rendered heterostyled is a highly remarkable phenomenon, as the two or three forms of the same undoubted species differ not only in important points of structure, but in the nature of their reproductive powers. As far as structure is concerned, the two sexes of many animals and of some plants differ to an extreme degree; and in both kingdoms the same species may consist of males, females, and hermaphrodites. Certain hermaphrodite cirripedes are aided in th

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POLYGAMOUS, DIOECIOUS, AND SUB-DIOECIOUS PLANTS.

POLYGAMOUS, DIOECIOUS, AND SUB-DIOECIOUS PLANTS.

Euonymus Europaeus (CELASTRINEAE). (Figure 7.12. Euonymus Europaeus Left: Hermaphrodite or male. Right: Female.) The spindle-tree is described in all the botanical works which I have consulted as an hermaphrodite. Asa Gray speaks of the flowers of the American species as perfect, whilst those in the allied genus Celastrus are said to be “polygamo- dioecious.” If a number of bushes of our spindle-tree be examined, about half will be found to have stamens equal in length to the pistil, with well-d

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GYNO-DIOECIOUS PLANTS.

GYNO-DIOECIOUS PLANTS.

The plants hitherto described either show a tendency to become dioecious, or apparently have become so within a recent period. But the species now to be considered consist of hermaphrodites and females without males, and rarely show any tendency to be dioecious, as far as can be judged from their present condition and from the absence of species having separated sexes within the same groups. Species belonging to the present class, which I have called gyno- dioecious, are found in various widely

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DICOTYLEDONS.

DICOTYLEDONS.

BORAGINEAE: Eritrichium. CONVOLVULACEAE: Cuscuta. SCROPHULARINEAE: Scrophularia. Linaria. Vandellia. ACANTHACEAE: Cryphiacanthus. Eranthemum. Daedalacanthus. Dipteracanthus. Aechmanthera. Ruellia. LABIATAE: Lamium. Salvia. NYCTAGINEAE: Oxybaphus. Nyctaginia. ASCLEPIADAE: Stapelia. CAMPANULACEAE: Specularia. Campanula. PRIMULACEAE: Hottonia. COMPOSITAE: Anandria. CRUCIFERAE: Heterocarpaea. VIOLACEAE: Viola. CISTINEAE: Helianthemum. Lechea. MALVEACEAE: Pavonia. MALPIGHIACEAE: Gaudichaudia. Aspicar

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MONOCOTYLEDONS.

MONOCOTYLEDONS.

JUNCEAE: Juncus. GRAMINEAE: Leersia. Hordeum. Cryptostachys. COMMELINEAE: Commelina. PONTEDERACEAE: Monochoria. ORCHIDEAE: Schomburgkia. Cattleya. Epidendron. Thelymitra. The first point that strikes us in considering this list of 55 genera, is that they are very widely distributed in the vegetable series. They are more common in the family of the Leguminosae than in any other, and next in order in that of the Acanthaceae and Malpighiaceae. A large number, but not all the species, of certain gen

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CONCLUDING REMARKS ON CLEISTOGAMIC FLOWERS.

CONCLUDING REMARKS ON CLEISTOGAMIC FLOWERS.

That these flowers owe their structure primarily to the arrested development of perfect ones, we may infer from such cases as that of the lower rudimentary petal in Viola being larger than the others, like the lower lip of the perfect flower,—from a vestige of a spur in the cleistogamic flowers of Impatiens,— from the ten stamens of Ononis being united into a tube,—and other such structures. The same inference may be drawn from the occurrence, in some instances, on the same plant of a series of

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