Part of a series of works by Darwin related to his theory of natural selection, the book is a study of carnivorous plants with specific attention paid to the adaptations that allow them to live in difficult conditions.[1] It includes illustrations by Darwin himself, along with drawings by his sons George and Francis Darwin.[2]
The book chronicles Darwin's experiments with various carnivorous plants, in which he carefully studied their feeding mechanisms.[3] Darwin tried several methods to stimulate the plants into activating their trap mechanisms, including feeding them meat and glass, blowing on them and prodding them with hair.[3] He found that only the movement of an animal would cause the plants to react, and concluded that this was an evolutionary adaptation to conserve energy for prey and to ignore stimuli that were not likely to be nutritious.[3] He also discovered that while some plants have distinct trap-like structures, others produce sticky fluids to ensnare their prey and concluded that this was an example of natural selection pressure resulting in various methods for food capture.[3]
The first edition had a reported printing of 3,000 copies. It was translated into several languages during Darwin's lifetime, including German.[1] A second English-language edition was published in 1888 after Darwin's death. It was edited with additions and footnotes by Francis Darwin.[2]
Summary
Drawing of a Venus flytrap, one of the plants Darwin studied, from the German translation
All page numbers refer to where the quotes can be found in the 1875, John Murray edition.
From his initial observations in 1860 of Drosera rotundifolia, the common sundew, Darwin developed a series of experiments ultimately establishing how "excellently adapted" these plants are to catching insects (p.3). Darwin knew that these plants flourish in nitrogen-limited environments, growing in bogs, poor peaty soil and moss (p.18). Most plants receive nutrients from the soil by their roots, but these plants have poor root systems and have adapted to receive nutrients (primarily nitrogenous substances) from captured insects.[4][5]
Darwin noted that Drosera and other carnivorous plants also feed on seeds, thus also making them vegetable feeders (p.134).
His notable observations are (p.3–4):
1. The sensitivity of the glands to slight pressure and to minute doses of nitrogenous substances. He noted that although there is extreme sensitivity it is wholly appropriate to the purpose of gaining sustenance, e.g. they do not respond to heavy rain falling on them nor to the wind blowing other leaves against them. They have adapted well to insects alighting upon them and this saves them from wasting energy through excess movement.
2. The power to digest nitrogenous substances by secreting digestive matter and then absorbing them. He noted that digestion follows a similar pattern to animal processes (p.135) in that acid is added to ferment the nutrient source(equivalent to pepsin). How they adapted this process from already existing substances in their system is explored later on in the book (p.361).
3. The changes which took place within the cells when the glands are excited in various ways. A major part of the book enumerates his experiments on Drosera rotundifolia. Darwin then turns his attention to other varieties of insectivorous plants and makes comparisons, noting that in some cases different parts of the leaf are used for digestion and others for absorption of decayed matter (p.330–331). He conjectured that plants may become adapted exclusively to one of these functions by gradually losing the other over a period of time. This would explain how Pinguicula and Utricularia came to use different functions even though they belong to the same family; p.331).
Darwin wrote in his autobiography that "the fact that a plant should secrete, when properly excited, a fluid containing an acid and ferment, closely analogous to the digestive fluid of an animal, was certainly a remarkable discovery."
Drosera, which is commonly known as the sundews, is one of the largest genera of carnivorous plants, with at least 194 species. These members of the family Droseraceae lure, capture, and digest insects using stalked mucilaginous glands covering their leaf surfaces. The insects are used to supplement the poor mineral nutrition of the soil in which the plants grow. Various species, which vary greatly in size and form, are native to every continent except Antarctica.
An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects.
Droseraceae is a family of carnivorous flowering plants, also known as the sundew family. It consists of approximately 180 species in three extant genera, the vast majority being in the sundew genus Drosera. The family also contains the well-known Venus flytrap and the more obscure waterwheel plant, both of which are the only living species of their respective genera. Representatives of the Droseraceae are found on all continents except Antarctica.
The Venus flytrap is a carnivorous plant native to the temperate and subtropical wetlands of North Carolina and South Carolina, on the East Coast of the United States. Although various modern hybrids have been created in cultivation, D. muscipula is the only species of the monotypic genus Dionaea. It is closely related to the waterwheel plant and the cosmopolitan sundews (Drosera), all of which belong to the family Droseraceae. Dionaea catches its prey—chiefly insects and arachnids—with a "jaw"-like clamping structure, which is formed by the terminal portion of each of the plant's leaves; when an insect makes contact with the open leaves, vibrations from the prey's movements ultimately trigger the "jaws" to shut via tiny hairs on their inner surfaces. Additionally, when an insect or spider touches one of these hairs, the trap prepares to close, only fully enclosing the prey if a second hair is contacted within (approximately) twenty seconds of the first contact. Triggers may occur as quickly as 1⁄10 of a second from initial contact.
Drosophyllum is a genus of carnivorous plants containing the single species Drosophyllum lusitanicum, commonly known as Portuguese sundew or dewy pine. In appearance, it is similar to the related genus Drosera, and to the much more distantly related Byblis.
Cephalotus is a genus which contains one species, Cephalotus follicularis the Albany pitcher plant, a small carnivorous pitcher plant. The pit-fall traps of the modified leaves have inspired the common names for this plant, which also include Western Australian pitcher plant, Australian pitcher plant, or fly-catcher plant. It is an evergreen herb that is endemic to peaty swamps in the southwestern corner of Western Australia. As with the unrelated Nepenthes, it catches its victims with pitfall traps.
Digestive enzymes take part in the chemical process of digestion, which follows the mechanical process of digestion. Food consists of macromolecules of proteins, carbohydrates, and fats that need to be broken down chemically by digestive enzymes in the mouth, stomach, pancreas, and duodenum, before being able to be absorbed into the bloodstream. Initial breakdown is achieved by chewing (mastication) and the use of digestive enzymes of saliva. Once in the stomach further mechanical churning takes place mixing the food with secreted gastric acid. Digestive gastric enzymes take part in some of the chemical process needed for absorption. Most of the enzymatic activity, and hence absorption takes place in the duodenum.
Byblis is a small genus of carnivorous plants, sometimes termed the rainbow plants for the attractive appearance of their mucilage-covered leaves in bright sunshine. Native to Australia and New Guinea, it is the only genus in the family Byblidaceae. The first species in the genus was described by the English botanist Richard Anthony Salisbury in 1808. Eight species are now recognised.
Roridula is a genus of evergreen, insect-trapping shrubs, with two species, of about 1⅓–2 m. It is the only genus in the family Roridulaceae. It has thin, woody, shyly branching, upright, initially brown, later grey stems, with lance- to awl-shaped leaves crowded at their tips. The star-symmetrical flowers consist from the outside in of five, green or reddish, free sepals, alternating with five white, pink or purple, free petals. Further to the middle and opposite the sepals are five stamens with the anthers initially kinked down. These suddenly flip up if the nectar-containing swelling at its base is being touched. The center of the flower is occupied by a superior ovary. The leaves and sepals carry many sticky tentacles of different sizes, that trap insects. Roridula does not break down the insect proteins, but bugs of the genus Pameridea prey on the trapped insects. These later deposit their feces on the leaves, which take up nutrients from the droppings. The species can be found in the Western Cape province of South Africa. They are commonly known as dewstick or fly bush in English and vlieëbos or vlieëbossie in Afrikaans.
Drosera capensis, commonly known as the Cape sundew, is a small rosette-forming carnivorous species of perennial sundew native to the Cape in South Africa. Because of its size, easy-to-grow nature, and the copious amounts of seed it produces, it has become one of the most common sundews in cultivation, and thus, one of the most frequently introduced and naturalised invasive Drosera species.
Drosera rotundifolia, the round-leaved sundew, roundleaf sundew, or common sundew, is a carnivorous species of flowering plant that grows in bogs, marshes and fens. One of the most widespread sundew species, it has a circumboreal distribution, being found in all of northern Europe, much of Siberia, large parts of northern North America, Korea and Japan but is also found as far south as California, Mississippi and Alabama in the United States of America and in New Guinea.
Drosera anglica, commonly known as the English sundew or great sundew, is a carnivorous flowering plant species belonging to the sundew family Droseraceae. It is a temperate species with a circumboreal range, although it does occur as far south as Japan, southern Europe, and the island of Kauai in Hawaii, where it grows as a tropical sundew. It is thought to originate from an amphidiploid hybrid of D. rotundifolia and D. linearis, meaning that a sterile hybrid between these two species doubled its chromosomes to produce fertile progeny which stabilized into the current D. anglica.
Drosera intermedia, commonly known as the oblong-leaved sundew, spoonleaf sundew, or spatulate leaved sundew, is an insectivorous plant species belonging to the sundew genus. It is a temperate or tropical species native to Europe, southeastern Canada, the eastern half of the United States, Cuba, Hispaniola, and northern South America.
A protocarnivorous plant, according to some definitions, traps and kills insects or other animals but lacks the ability to either directly digest or absorb nutrients from its prey like a carnivorous plant. The morphological adaptations such as sticky trichomes or pitfall traps of protocarnivorous plants parallel the trap structures of confirmed carnivorous plants.
Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods, and occasionally small mammals and birds. They still generate all of their energy from photosynthesis. They have adapted to grow in waterlogged sunny places where the soil is thin or poor in nutrients, especially nitrogen, such as acidic bogs. They can be found on all continents except Antarctica, as well as many Pacific islands. In 1875, Charles Darwin published Insectivorous Plants, the first treatise to recognize the significance of carnivory in plants, describing years of painstaking research.
Drosera uniflora is a species in the carnivorous plant genus Drosera that is native to southern Chile, Argentina, and the Falkland Islands. It is a tiny sundew with a solitary white flower as its name would suggest. Stalked glands on its leaves, which secrete sticky mucilage at the tips, are used to capture and hold insect prey, from which the plant derives the nutrients it cannot obtain in sufficient quantity from the soil. It was formally described in 1809 by botanist Carl Ludwig Willdenow.
Nepenthesin is an aspartic protease of plant origin that has so far been identified in the pitcher secretions of Nepenthes and in the leaves of Drosera peltata. It is similar to pepsin, but differs in that it also cleaves on either side of Asp residues and at Lys┼Arg. While more pH and temperature stable than porcine pepsin A, it is considerably less stable in urea or guanidine hydrochloride. It is the only known protein with such a stability profile.
Pinguicula, commonly known as butterworts, is a genus of carnivorous flowering plants in the family Lentibulariaceae. They use sticky, glandular leaves to lure, trap, and digest insects in order to supplement the poor mineral nutrition they obtain from the environment. Of the roughly 80 currently known species, 13 are native to Europe, 9 to North America, and some to northern Asia. The largest number of species is in South and Central America.
The tissues that are concerned with the secretion of gums, resins, volatile oils, nectar latex, and other substances in plants are called secretory tissues. These tissues are classified as either laticiferous tissues or glandular tissues.
Toxomerus basalis, commonly known as the sundew flower fly, is a species of kleptoparasitic fly endemic to Brazil. It was first described by Francis Walker in 1836. It feeds on captured, immobilized insects caught on the sticky leaves of sundew plants, which are carnivorous. Adult flies seem to have some capacity to escape from Drosera leaves if they have not come into contact with too many of the tentacles. The species is non-specific and have been found on large-leaved, semi-erect, and thread-like Drosera species, such as Drosera graomogolensis and Drosera magnifica.
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