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Tropaeolum majus

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Introduction

appearing in a single generation from the closest possible interbreeding, that is between brothers and sisters, I thought that the same rule would hold good with plants; and that it would be necessary to self-fertilise and cross them plants during several successive generations, at the sacrifice of too much time, in order to preserve arrive at any difference in the offspring result. I ought to have reflected that such elaborate provisions favouring cross-fertilisation, as we see in innumerable plants, would not have been acquired for the sake of gaining a distant and slight advantage, or of avoiding a distant and slight evil. Moreover the fertilisation of a flower by its own pollen is a closer degree of self-fertilisation inter-breeding than is possible with ordinary unisexual animals; so that the same an earlier result might not follow have been expected. I was at last led to make the experiments recorded in the present volume from the following cir=

[Cross and self fertilisation, p. 8: "It often occurred to me that it would be advisable to try whether seedlings from cross-fertilised flowers were in any way superior to those from self-fertilised flowers. But as no instance was known with animals of any evil appearing in a single generation from the closest possible interbreeding, that is between brothers and sisters, I thought that the same rule would hold good with plants; and that it would be necessary at the sacrifice of too much time to self-fertilise and intercross plants during several successive generations, in order to arrive at any result. I ought to have reflected that such elaborate provisions favouring cross-fertilisation, as we see in innumerable plants, would not have been acquired for the sake of gaining a distant and slight advantage, or of avoiding a distant and slight evil. Moreover, the fertilisation of a flower by its own pollen corresponds to a closer form of interbreeding than is possible with ordinary bi-sexual animals; so that an earlier result might have been expected. I was at last led to make the experiments recorded in the present volume from the following circumstance."]

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1799. p. 202) "nature-intended that a sexual intercourse should take place between neighbouring plants of the same species." After alluding to the various means by which pollen is transported from flower to flower, as far as was then imperfectly known, he adds "that nature has something more in view than that its own proper males should fecundate each blossom." In 1811 Kölreuter plainly hinted at the same law, as did afterwards another famous hybridiser of plants, Herbert.* But none of these distinguished observer appear to have been

[Cross and self fertilisation, p. 7: "Andrew Knight saw the truth much more clearly, for he remarks,† "Nature intended that a sexual intercourse should take place between neighbouring plants of the same species." After alluding to the various means by which pollen is transported from flower to flower, as far as was then imperfectly known, he adds, "Nature has something more in view than that its own proper males would fecundate each blossom." In 1811 Kölreuter plainly hinted at the same law, as did afterwards another famous hybridiser of plants, Herbert.‡ But none of these distinguished observers appear to have been sufficiently impressed with the
† 'Philosophical Transactions' 1799 page 202.
‡ Kölreuter 'Mém. de l'Acad. de St. Pétersbourg' tom. iii. 1809 published 1811 page 197. After showing how well the Malvaceae are adapted for cross-fertilisation, he asks, "An id aliquid in recessu habeat, quod hujuscemodi flores nunquam proprio suo pulvere, sed semper eo aliarum suae speciei impregnentur, merito quaeritur? Certe natura nil facit frustra." Herbert, 'Amaryllidaceae, with a Treatise on Cross-bred Vegetables' 1837."]

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Heliotropism

Tropaeolum majus

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Introduction

these plants are frequently inter-crossed, owing to the prepotency of pollen from another individual or variety over that from the same plant.

As plants are adapted by so many and such diversified & effective means for cross-fertilisation, it might safely have been inferred that they derived some benefit great advantage from this process; and it is the object of the present work to show the nature and greatness importance of the benefits thus derived. There are, however some exceptions to the general rule of plants being constructed so as to allow of or to favour cross-fertilisation; for some few plants seem to be invariably self-fertilised; yet even these generally retain indications that they were once traces of having been formerly adapted for cross-fertilisation. These exceptions need not make us doubt about the meaning truth of the general rule, any more than the existence of some few plants which although bearing flowers never set seed, should make us doubt, that flowers with their male and

[Cross and self fertilisation, pp. 2-3: "Lastly, there is a large class in which the flowers present no apparent obstacle of any kind to self-fertilisation, nevertheless these plants are frequently intercrossed, owing to the prepotency of pollen from another individual or variety over the plant's own pollen.
As plants are adapted by such diversified and effective means for cross-fertilisation, it might have been inferred from this fact alone that they derived some great advantage from the process; and it is the object of the present work to show the nature and importance of the benefits thus derived. There are, however, some exceptions to the rule of plants being constructed so as to allow of or to favour cross-fertilisation, for some few plants seem to be invariably self-fertilised; yet even these retain traces of having been formerly adapted for cross-fertilisation. These exceptions need not make us doubt the truth of the above rule, any more than the existence of some few plants which produce flowers, and yet never set seed, should make us doubt that flowers are adapted for the production of seed and the propagation of the species."]