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Darwin’s Books on Plant Biology

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Darwin’s pioneering books on plant biology provided key evidence for his theory that natural selection was the driving force of evolution. These books appeared between 1862 and 1881.


On the Various Contrivances by which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing (1862)
Darwin pioneered work on orchid biology in his two books (1862 and 1877) on the fertilization of orchids by insects. He demonstrated that highly specialized adaptations in orchid flowers assure that any bee, moth, or other pollinator had to “fit” the mechanism presented to it. Darwin summarized his survey of the diverse “contrivances” orchids evolved to assure cross-fertilization by insects by stating that “Nature thus tells us, in the most emphatic manner, that she abhors perpetual self-fertilisation.”

The Movements and Habits of Climbing Plants (1865)
Although Hugo von Mohl and Ludwig Palm had written in 1827 a couple of ground-breaking papers on climbing plants in Germany, Darwin after years of meticulous observations compiled data on various ways that species across a wide range of families and orders could climb over other objects, including other plants, to compete for light with their neighbors. He singled out stem twiners, those that used the petioles of leaves or developed actual tendrils, and others – like ivy – that produced rootlets to support his contention that natural selection had favored those species with these adaptations to survive in sun-deprived habitats.

The Variation of Animals and Plants Under Domestication, Vol. 1 (1868)
The Variation of Animals and Plants Under Domestication, Vol. 2 (1868)
Darwin used these books to compile information on livestock breeding, floricultural and horticultural breeding, fanciers of pets – for example, pigeons & other birds, dogs, and cats – to demonstrate that artificial selection by human beings for certain desired traits was long-standing practice in human cultures. He created the analogy between this so-called artificial selection to natural selection of adaptable variations in populations by natural forces that has occurred from the origin of life to the present day, thus producing new species, while the unsuccessful ones went extinct. Unfortunately, a reasonable explanation of the hereditary mechanisms producing the variation eluded him and his peers, until the early 1900s. It was then that biologists rediscovered Mendel’s paper on heredity in an obscure Bohemian journal and established the beginning of modern genetic research.

Insectivorous Plants (1875)
Today there are just about 600 carnivorous plant species, which have evolved independently in six sub-classes. Their common adaptation is that their leaves were transformed into organs for capturing & digesting insects & small invertebrates. Why so many diverse species evolved these adaptations was in order to survive in nutrient-poor habitats, which Darwin was first to propose. He concluded this from his experiments at home and in his greenhouse, when he saw their growth was promoted when nitrogen-rich materials were fed to them. This work led to a new emphasis in the early twentieth century on plant nutrition studies, leading ultimately to the biochemical analyses for such research, especially on plant enzymes.

The Effects of Cross and Self Fertilisation in the Vegetable Kingdom (1876)
The Different Forms of Flowers on Plants of the Same Species (1877)
These books were the culmination of a series of researches between 1860 and 1877 on the subject of fertility, selective advantage, and heredity in the flowering plants. Darwin showed that cross-pollination (out-breeding) was the norm in plants; thus, he helped dispel the then-commonly held notion of botanists that most plants pollinated themselves. Anatomical, morphological, or behavioral mechanisms that maximized out-breeding and minimized in-breeding were favored by Natural Selection. He showed this in orchids, and in a wide variety of families and orders of the plant kingdom. His meticulous studies of dimorphism in species of Primula and trimorphism in Lythrum salicaria and species of genera like Oxalis, working out details in the so-called legitimate and illegitimate crossings of these kinds of flowers gave him some of his greatest satisfaction.

The Power of Movement in Plants (1880)
In Darwin’s final plant book, he concluded that the leaves, stems, branches, and roots of so many plants move in a circular fashion, which he named circumnutation. The vining habit found in so many plant groups evolved special adaptations for twining from the power of movement already inherent in the plant body. German physiologists had already noted the effect and turgor pressure in cells was implicated; what Darwin hoped to find was some mechanism by which the sleep movements in leaves, for one example, happened. Francis Darwin, his son who helped him in so many of these experiments, carried on studies of leaf stomata at University of Cambridge. Some other studies of phototropism, geotropism, and thigmotropism that are recorded in the book led to physiological research in the twentieth century on plant hormones and their part in these phenomena, as well as in flowering, fruit set, fruit ripening – phenomena basic to academic and practical horticulture and agriculture.

The Formation of Vegetable Mould, Through The Action of Worms, with Observations on Their Habits (1881)
Darwin’s last book came from 40 years observing the action of earthworms on soil turnover and the making of topsoil, called in those days “vegetable mould.” Josiah Wedgewood II, then Darwin’s uncle, later his father-in-law, suggested he attend to the work of earthworms in soil turnover and burying of old shards in a field near the pottery. Charles was visiting there after returning from the Voyage of the Beagle in 1836. Today Darwin is recognized as “the first scientist to bring earthworms to the attention of scientists and the general public,” noting particularly their importance “in the history of the world” (Darwin’s words) – “in breaking down dead plant materials, recycling the nutrients they contain, and turning over the soil.” This work alone spawned the late 19th and early 20th century upsurge in research into the biology and ecology of earthworms. For more on the subject, please see The Earth Moved: on the remarkable achievements of earthworms by Amy Stewart (2004).

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