The Different Forms of Flowers on Plants of the Same Species

Last updated

The Different Forms of Flowers on Plants of the Same Species is a book by Charles Darwin first published in 1877. [1] It is the fifth of his six books devoted solely to the study of plants (excluding The Variation of Animals and Plants Under Domestication [2] ).

Contents

Context

These writings contributed to Darwin's pursuit of evidence that would support his theory of natural selection. There were only two more books to follow: The Power of Movement in Plants (1880) and The Formation of Vegetable Mould through the Action of Worms (1881). He conducted a wide range of experiments and observations and the results of these form the framework of the book. He was assisted in this work by his son, Francis Darwin who also wrote a preface for the second edition which was published two years after his father's death in 1882. The book was dedicated to his longtime friend and colleague, Harvard botany professor Asa Gray "as a small tribute of respect and affection". [3]

The work

Using the four classifications established by Carl Linnaeus (hermaphroditic, monoecious, dioecious, polygamous), Darwin concentrated on two divisions of the hermaphroditic class, namely the cleistogamic and heterostyled.

Darwin’s reflections indicate the economy of nature through a process of gradual modification of plants, their structures being modified and degraded for the purpose of the large scale production of seed which is necessary and advantageous for survival. Darwin states (p. 227): "Cleistogamic flowers ... are admirably fitted to yield a copious supply of seed at a wonderfully small cost to the plant."

Francis Darwin indicated that the work on heterostyly had given his father extreme pleasure, especially as it had been one of the most puzzling bits of work he ever carried out. Darwin thought that hardly anyone had seen the full importance of heterostyly.

Summary.

In 1883, Alfred Russel Wallace wrote a tribute to Darwin (entitled 'The Debt of Science to Darwin’) who had died the year before. One such tribute appeared in 'The Century', an illustrated monthly magazine. As part of this article he included a summary of Darwin's work relating to this book (p. 428):

"The cowslip (Primula veris) has two kinds of flowers in nearly equal proportions: in the one the stamens are long and the style short, and in the other the reverse, so that in one the stamens are visible at the mouth of the tube of the flower, in the other the stigma occupies the same place, while the stamens are halfway down the tube. The fact had been known to botanists for 70 years, but had been classed as a case of mere variability, and therefore considered to be of no importance. In 1860 Darwin set to find out what it meant, since, according to his views, a definite variation like this must have a purpose. After a considerable amount of observation and experiment, he found that bees and moths visited the flowers, and that their proboscis become covered with pollen while sucking up the nectar, and further, the pollen of a long stamened plant would most surely be deposited on the stigma of the long styled plants, and vice versa. Now followed a long series of experiments, in which cowslips were fertilised with either pollen from the same kind or from a different kind of flower, and the invariable result was that the crosses between the two different types of flowers produced more good capsules, and more seed in each capsule; and as these crosses would be most frequently effected by insects, it was clear that this curious arrangement directly served to increase the fertility of this common plant. The same thing was found to occur in the primrose, as well as in flax (Linum perenne), lungworts (Pulmonaria), and a host of other plants, including the American partridge-berry (Mitchella repens). These are called dimorphic heterostyled plants.

Still more extraordinary is the case of the common loosestrife (Lythrum salicaria), which has both stamens and styles of three distinct lengths, each flower having two sets of stamens and one style, all of different lengths, and arranged in three different ways:

  1. A short style, with six medium and six long stamens;
  2. A medium style, with six short and six long stamens;
  3. A long style, with six medium and six short stamens.

These flowers can be fertilised in eighteen distinct ways, necessitating a vast number of experiments, the result being, as in the case of the cowslip, that flowers fertilised by the pollen from stamens of the same length as the styles, gave on the average a larger number of capsules and a very much larger number of seeds than in any other case. The exact correspondence in the length of the style of each form with that of one set of stamens in the other form insures that the pollen attached to any part of the body of an insect shall be applied to a style of the same length on another plant, and there is thus a triple chance of the maximum of fertility....There is thus the clearest proof that these complex arrangements have the important end of securing both a more abundant and more vigorous offspring.”

Observations and experiments still continue today to further the understanding of this phenomenon instigated by Darwin in this original and seminal work.

Related Research Articles

<span class="mw-page-title-main">Fertilisation</span> Union of gametes of opposite sexes during the process of sexual reproduction to form a zygote

Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. While processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.

<span class="mw-page-title-main">Pollination</span> Biological process occurring in plants

Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, for example beetles; birds, butterflies, and bats; water; wind; and even plants themselves. Pollinating animals travel from plant to plant carrying pollen on their bodies in a vital interaction that allows the transfer of genetic material critical to the reproductive system of most flowering plants. When self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species, it can produce hybrid offspring in nature and in plant breeding work.

<span class="mw-page-title-main">Self-pollination</span> Form of pollination

Self-pollination is a form of pollination in which pollen from the same plant arrives at the stigma of a flower or at the ovule. There are two types of self-pollination: in autogamy, pollen is transferred to the stigma of the same flower; in geitonogamy, pollen is transferred from the anther of one flower to the stigma of another flower on the same flowering plant, or from microsporangium to ovule within a single (monoecious) gymnosperm. Some plants have mechanisms that ensure autogamy, such as flowers that do not open (cleistogamy), or stamens that move to come into contact with the stigma. The term selfing that is often used as a synonym, is not limited to self-pollination, but also applies to other type of self-fertilization.

<span class="mw-page-title-main">Plant reproductive morphology</span> Parts of plant enabling sexual reproduction

Plant reproductive morphology is the study of the physical form and structure of those parts of plants directly or indirectly concerned with sexual reproduction.

<i>Primula vulgaris</i> Species of flowering plant

Primula vulgaris, the common primrose, is a species of flowering plant in the family Primulaceae, native to western and southern Europe, northwest Africa, and parts of southwest Asia. The common name is primrose, or occasionally common primrose or English primrose to distinguish it from other Primula species also called primroses. None of these are closely related to the evening primroses.

<span class="mw-page-title-main">Heterostyly</span> Two different types of flowers (style) on same plant

Heterostyly is a unique form of polymorphism and herkogamy in flowers. In a heterostylous species, two or three morphological types of flowers, termed "morphs", exist in the population. On each individual plant, all flowers share the same morph. The flower morphs differ in the lengths of the pistil and stamens, and these traits are not continuous. The morph phenotype is genetically linked to genes responsible for a unique system of self-incompatibility, termed heteromorphic self-incompatibility, that is, the pollen from a flower on one morph cannot fertilize another flower of the same morph.

<span class="mw-page-title-main">Velloziaceae</span> Family of flowering plants

Velloziaceae is a family of monocotyledonous flowering plants. The APG II system, of 2003, also recognizes this family, and assigns it to the order Pandanales.

<span class="mw-page-title-main">Flower</span> Reproductive structure in flowering plants

A flower, also known as a bloom or blossom, is the reproductive structure found in flowering plants. Flowers consist of a combination of vegetative organs – sepals that enclose and protect the developing flower, petals that attract pollinators, and reproductive organs that produce gametophytes, which in flowering plants produce gametes. The male gametophytes, which produce sperm, are enclosed within pollen grains produced in the anthers. The female gametophytes are contained within the ovules produced in the carpels.

<span class="mw-page-title-main">Proteaceae</span> Family of flowering plants

The Proteaceae form a family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genera with about 1,660 known species. Australia and South Africa have the greatest concentrations of diversity. Together with the Platanaceae, Nelumbonaceae and in the recent APG IV system the Sabiaceae, they make up the order Proteales. Well-known 'Proteaceae genera include Protea, Banksia, Embothrium, Grevillea, Hakea and Macadamia. Species such as the New South Wales waratah, king protea, and various species of Banksia, Grevillea, and Leucadendron are popular cut flowers. The nuts of Macadamia integrifolia are widely grown commercially and consumed, as are those of Gevuina avellana on a smaller scale.

Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.

Tristyly is a rare floral polymorphism that consists of three floral morphs that differ in regard to the length of the stamens and style within the flower. This type of floral mechanism is thought to encourage outcross pollen transfer and is usually associated with heteromorphic self-incompatibility to reduce inbreeding. It is an example of heterostyly and reciprocal herkogamy, like distyly, which is the more common form of heterostyly. Darwin first described tristylous species in 1877 in terms of the incompatibility of these three morphs.

This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.

This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology. For other related terms, see Glossary of phytopathology, Glossary of lichen terms, and List of Latin and Greek words commonly used in systematic names.

<i>Fertilisation of Orchids</i> 1862 book by Charles Darwin

Fertilisation of Orchids is a book by English naturalist Charles Darwin published on 15 May 1862 under the full explanatory title On the Various Contrivances by Which British and Foreign Orchids Are Fertilised by Insects, and On the Good Effects of Intercrossing. Darwin's previous book, On the Origin of Species, had briefly mentioned evolutionary interactions between insects and the plants they fertilised, and this new idea was explored in detail. Field studies and practical scientific investigations that were initially a recreation for Darwin—a relief from the drudgery of writing—developed into enjoyable and challenging experiments. Aided in his work by his family, friends, and a wide circle of correspondents across Britain and worldwide, Darwin tapped into the contemporary vogue for growing exotic orchids.

Xenogamy is the transfer of pollen grains from the anther to the stigma of a different plant. This is the only type of cross pollination which during pollination brings genetically different types of pollen grains to the stigma.

<i>Veronica strictissima</i> Species of flowering plant in the family Plantaginaceae

Veronica strictissima, the Banks Peninsula hebe, is a species of flowering plant in the family Plantaginaceae. It is only found on Banks Peninsula in New Zealand.

Sexual selection is described as natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Sexual selection is a common concept in animal evolution but, with plants, it is oftentimes overlooked because many plants are hermaphrodites. Flowering plants show many characteristics that are often sexually selected for. For example, flower symmetry, nectar production, floral structure, and inflorescences are just a few of the many secondary sex characteristics acted upon by sexual selection. Sexual dimorphisms and reproductive organs can also be affected by sexual selection in flowering plants.

<span class="mw-page-title-main">Mixed mating systems</span> Plants which reproduce in multiple ways

A mixed mating system, also known as “variable inbreeding” a characteristic of many hermaphroditic seed plants, where more than one means of mating is used. Mixed mating usually refers to the production of a mixture of self-fertilized (selfed) and outbred (outcrossed) seeds. Plant mating systems influence the distribution of genetic variation within and among populations, by affecting the propensity of individuals to self-fertilize or cross-fertilize . Mixed mating systems are generally characterized by the frequency of selfing vs. outcrossing, but may include the production of asexual seeds through agamospermy. The trade offs for each strategy depend on ecological conditions, pollinator abundance and herbivory and parasite load. Mating systems are not permanent within species; they can vary with environmental factors, and through domestication when plants are bred for commercial agriculture.

Reproductive assurance occurs as plants have mechanisms to assure full seed set through selfing when outcross pollen is limiting. It is assumed that self-pollination is beneficial, in spite of potential fitness costs, when there is insufficient pollinator services or outcross pollen from other individuals to accomplish full seed set.. This phenomenon has been observed since the 19th century, when Darwin observed that self-pollination was common in some plants. Constant pollen limitation may cause the evolution of automatic selfing, also known as autogamy. This occurs in plants such as weeds, and is a form of reproductive assurance. As plants pursue reproductive assurance through self-fertilization, there is an increase in homozygosity, and inbreeding depression, due to genetic load, which results in reduced fitness of selfed offspring. Solely outcrossing plants may not be successful colonizers of new regions due to lack of other plants to outcross with, so colonizing species are expected to have mechanisms of reproductive assurance - an idea first proposed by Herbert G. Baker and referred to as Baker's "law" or "rule". Baker's law predicts that reproductive assurance affects establishment of plants in many contexts, including spread by weedy plants and following long-distance dispersal, such as occurs during island colonization. As plants evolve towards increase self-fertilization, energy is redirected to seed production rather than characteristics that increased outcrossing, such as floral attractants, which is a condition known as the selfing syndrome.

<span class="mw-page-title-main">Distyly</span>

Distyly is a type of heterostyly in which a plant demonstrates reciprocal herkogamy. This breeding system is characterized by two separate flower morphs, where individual plants produce flowers that either have long styles and short stamens, or that have short styles and long stamens. However, distyly can refer to any plant that shows some degree of self-incompatibility and has two morphs if at least one of the following characteristics is true; there is a difference in style length, filament length, pollen size or shape, or the surface of the stigma. Specifically these plants exhibit intra-morph self-incompatibility, flowers of the same style morph are incompatible. Distylous species that do not exhibit true self-incompatibility generally show a bias towards inter-morph crosses - meaning they exhibit higher success rates when reproducing with an individual of the opposite morph.

References

  1. ↑ Darwin, Charles (1877). he Different Forms of Flowers on Plants of the Same Species. London: John Murray. Retrieved 10 April 2023.
  2. ↑ Darwin, Charles (1868). The Variation of Animals and Plants Under Domestication. London: John Murray.
  3. ↑ Dupree, A. Hunter (1988). Asa Gray, American Botanist, Friend of Darwin. Baltimore, MD: Johns Hopkins University Press. p. 356. ISBN   978-0-801-83741-8.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.