The Different Forms of Flowers on Plants of the same Species.

London: John Murray, 1877.

First edition, an exceptionally fine copy, entirely unopened, of Darwin’s important work on the adaptation of plants; the edges have been specially trimmed by the binder for presentation. “Why do flowers, the reproductive organs of angiosperms, exhibit such astonishing diversity in form when they have a single primary function—to ensure mating and reproductive success? The answer lies in the immobility of plants and their requirement for pollen vectors (animals, wind, water) to transport male gametes between individuals resulting in cross-pollination. Today the great structural variety of flowers is largely interpreted as the historical outcome of natural selection during interactions with diverse pollen vectors resulting in floral adaptation. Charles Darwin was the originator of this idea … it was not until Charles Darwin fully turned his attention to plants after taking up residence at Down House in 1842 that the careful, but largely scattered, observations of the early naturalists began to be understood within a single framework, that of evolutionary biology, and specifically, the evolution of adaptation by natural selection. Darwin’s studies on floral mechanisms that promote cross-pollination, the consequences of cross- versus self-fertilization on offspring performance, and the evolution and function of sexual polymorphisms were presented, respectively, in three influential books. These works helped to provide the conceptual foundation for future research in plant reproductive biology and many of Darwin’s ideas have remained resilient to modern scrutiny” (Barrett, p. 351). “This book consists chiefly of the several papers on hetero-styled flowers originally published by the Linnean Society, corrected, with much new matter added, together with observations on some other cases in which the same plant bears two kinds of flowers. As before remarked, no little discovery of mine ever gave me so much pleasure as the making out the meaning of hetero-styled flowers. The results of crossing such flowers in an illegitimate manner, I believe to be very important, as bearing on the sterility of hybrids; although these results have been noticed by only a few persons” (Autobiography). In these investigations, Darwin crosses a ‘long-styled’ individual with another long-styled flower to produce a comparatively infertile primrose, illustrating a degree of sterility within the limits of a single species comparable to that produced in the crossing of distinct species. Darwin’s work on hetero-styled plants bears on one of the most difficult points in the statement of the case for evolution, the sterility of interspecific crosses and of hybrids. In Desmond and Moore’s view, Forms of Flowers capped his work on nature’s complex ‘marriage arrangements’. “It was a botanical voyeur’s diary. He had contrived all sorts of liaisons among the blossoms, spying on them through his eyeglass. After endless manual pollinations, myriad microscopic seed-counts, he described the results with due delicacy, showing how ‘legitimacy’ was conferred on cross-fertilisations. Even before the first reviews appeared, he was wrapped up in his next book on plant movements” (p. 628). Very rare in such fine condition.

“On return from his voyage around the world on H.M.S. Beagle (1831–36), Darwin spent a few years in London during which time he published The Voyage of the Beagle (1839) and, in the same year, married his first cousin Emma Wedgwood. In 1842 ill-health forced him to move to the village of Downe in Kent where he would spend the rest of his life with his family working in near seclusion at Down House. The early years were taken up with various projects including a monograph on coral reefs, studies on barnacles and the accumulation of evidence culminating in the publication of the Origin of Species (1859). Also, during this time Darwin began to work diligently on plants and his interests grew to the point where he dedicated much of his later life to botanical pursuits. Darwin was always a reluctant botanist, often pointedly referring to his inadequate knowledge of plants when compared with his ‘expert’ botanical colleagues and correspondents. Nevertheless, despite this modesty Darwin published numerous articles on plants and six botanical works. Indeed, it has been claimed that during his scientific career Darwin spent more time working on plants than any other group of organisms. Today it is recognized that Darwin made original and influential contributions to the development of plant science.

“Why did Darwin devote over 40 years of his life to working on plants, much of it on reproductive biology? A variety of influences were surely responsible. Foremost were Darwin’s ill-health, restricting travel and the types of work he could conduct, and an established family interest in growing plants. His grandfather Erasmus Darwin wrote an influential botanical text and his father Robert maintained a garden and tropical plant collection at his home (‘The Mount’) in Shrewsbury. The young Charles helped in the garden and was encouraged to record information on plants in his father’s collection. Darwin’s most influential mentors—Professor John Stevens Henslow at Cambridge and Sir Joseph Dalton Hooker at Kew—were botanists and they no doubt encouraged Darwin to consider plants as suitable subject material for evaluating his developing ideas on variation and evolution. Henslow in particular was especially interested in variation within species and this may have been influential. With a large garden and glasshouse at Down House, and the assistance of gardeners, plants were easy to grow and amenable to direct observation and experimentation. This no doubt satisfied Darwin’s natural curiosity and his practical leanings. Beginning in 1841 he began publishing short articles in Gardener’s Chronicle, the leading journal of gardeners and nurserymen. He later summarized much of his work on domesticated plants in the volume The Variation of Animals and Plants under Domestication (1868). Darwin was also a prolific correspondent and because plant material, especially seeds, could easily be sent to him from many parts of the world he was able to grow many ‘foreign’ species at Down House, increasing his appreciation of plant diversity. Finally, as is evident from their increasing inclusion in later editions of the Origin of Species, plants provided outstanding subjects for evaluating his ideas on the evolution of adaptation and the importance of outcrossing for maintaining variation. Indeed, in a letter to J. D. Hooker on 3 June 1857, he confessed that he found ‘any proposition more readily tested in botanical work … than zoological’ (Autobiography)…

“Darwin’s last book on plant reproductive biology The Different Forms of Flowers on Plants of the same Species (1877) is the widest ranging in scope … Although it has a particular focus on polymorphic sexual systems it integrates diverse sources of evidence from comparative morphology, compatibility studies, pollination biology, ecology and studies of inheritance. Six chapters are devoted to heterostylous floral polymorphisms, one to dioecy and related gender strategies, and the final chapter discusses species that are predominantly selfing through the formation of cleistogamous (closed) flowers. Darwin obtained immense pleasure from his studies of heterostyly on which he also published separate journal articles. In Darwin’s autobiographical recollections, he states: ‘I do not think anything in my scientific life has given me so much satisfaction as making out the meaning of the structure of heterostylous flowers’. Darwin provided the first functional interpretation of the adaptive significance of heterostyly and speculated on the evolutionary pathway leading to the evolution of distyly … our understanding of stylar polymorphisms has broadened considerably to include a diversity of novel forms; however, all these can be accommodated within Darwin’s general functional interpretation involving proficient animal-mediated cross-pollination.

“A remarkable feature of Forms of Flowers is the extent to which Darwin identified general phenomena and concepts that form the basis of considerable contemporary research … Reasoned arguments based on diverse sources of evidence are the defining feature of Darwin’s scientific approach. His three books involved careful observations, manipulative experiments, extensive data collection and thoughtful evolutionary inference. Few biologists of the time used these approaches in solving problems and most botanical studies relevant to ecology and evolutionary biology were descriptive in nature and remained so for some time after Darwin died in 1882. Indeed, it was not until the birth of population biology in the 1960s and 1970s that plant reproductive biology experienced a true renaissance, with theoretical models guiding experimental field studies of plant populations …

“Darwin’s Forms of Flowers largely focused on plants with sexual polymorphisms in which populations are reproductively sub-divided into distinct mating groups. These may be morphologically indistinguishable, as in the different classes of homomorphic incompatibility, or, as with heterostyly, there are distinct morphological phenotypes or ‘morphs’. Darwin worked primarily on distyly and tristyly, but since then four additional stylar polymorphisms have been recognized … Darwin reported the occurrence of heterostyly from 14 families and 38 genera … Darwin was particularly intrigued by the evolution and function of heterostyly commenting that ‘The existence of plants which have been rendered heterostyled is a highly remarkable phenomenon’ (p. 275). Although he was not confident about the evolutionary pathway(s) leading to the evolution of heterostyly, admitting that ‘This is a very obscure subject, on which I can throw little light, but which is worthy of discussion’ (p. 260), he was more certain, based on his own experimental studies of Primula, Linum and Lythrum, about the functional significance of heterostyly. ‘We may feel sure that plants have been rendered heterostyled to ensure cross-fertilisation’ (p. 258). Darwin interpreted the reciprocal positions of anthers and stigmas (reciprocal herkogamy) in the style morphs of heterostylous populations as a floral mechanism promoting animal-mediated cross-pollination through segregated pollen deposition on the bodies of pollinators …

“The evolutionary origins of heterostyly remain poorly understood … As Darwin surmised (p. 261), an early stage involving variation in stigma height (but not anther height) appears to precede the establishment of distyly. However, we are still some way from obtaining a clear picture of the stages in the build up of the polymorphism, especially the order in which the morphological polymorphisms and heteromorphic incompatibility are assembled. This problem is because of the difficulties of inferring ancestral states in phylogenies and the finding that heterostyly often appears to be basal in the lineages that have been examined, as Darwin also recognized. ‘In some of these families the heterostyled condition must have been acquired at a very remote period … and it is not probable that each species acquired its heterostyled structure independently of it close allies … [but] must have inherited their structure from a common progenitor’ (p. 255) …

“In chapter seven of Forms of Flowers Darwin focused his attention on the evolution of separate sexes (dioecy) and related gender strategies, particularly gynodioecy. It is clear that he considered that a neat division of sexual systems into Linnean categories masked considerable variability of potential evolutionary importance. Indeed, at the very beginning of the book Darwin drew attention to this problem: ‘As far as the sexual relations of flowers are concerned, Linnaeus long ago divided them into hermaphrodite, monoecious, dioecious and polygamous species … but the classification is artificial, and the groups often pass into one another(p. 1). Darwin may have considered the merging of sexual systems as evidence for his general thesis that most evolutionary change was gradual and involved small incremental steps resulting from natural selection. For example he noted that ‘various hermaphrodite plants have become or are becoming dioecious by many and excessively small steps’ (p. 281) and ‘This case (Euonymus europaeus) appears to me very interesting, as showing how gradually an hermaphrodite plant may be converted into a dioecious one(p. 292). In chapter seven Darwin tries to make sense of plant sexual diversity and clearly shows that in some groups sexual systems sometimes do not exhibit tidy boundaries.

“Although dioecy is relatively infrequent in angiosperms, occurring in approximately 6 per cent of species, the polymorphism has evolved repeatedly from hermaphroditism, with at least 100 independent origins. Understanding how and why this transition occurs continues to attract attention from evolutionary biologists. Darwin considered the selective mechanisms responsible for the evolution of dioecy a particularly thorny problem stating that ‘There is much difficulty in understanding why hermaphrodite plants should ever have been rendered dioecious’ (p. 279). Interestingly, given the main conclusion of his book on Effects of Cross and Self-fertilization (1876), Darwin rejected the idea that dioecy is favoured because of the outbreeding advantage unisexuals may enjoy over hermaphrodites. ‘As we must assume that cross-fertilisation was assured before an hermaphrodite could be changed into a dioecious plant, we may conclude that the conversion has not been effected for the sake of gaining the great benefits which follow from cross-fertilisation’ (p. 279). Instead, Darwin emphasized the resource costs of combined sex functions under stressful environmental conditions to explain why unisexual plants may be favoured …

“Darwin’s main contribution to plant reproductive biology was his recognition that much of the extraordinary diversity in floral form can be explained by natural selection of mechanisms promoting cross-pollination and reducing the incidence of self-fertilization and its harmful effects on offspring. In addition he also recognized that evolutionary history plays an important role in guiding future evolutionary change. ‘The wonderful diversity of the means for gaining the same end [cross-fertilisation] … depends on the nature of all the previous changes through which the species had passed, and on the more or less complete inheritance of the successive adaptations of each part to the surrounding conditions’ (p. 258) …

“Not all of Darwin’s ideas on plant reproductive biology are still valid today. For example, although Darwin was one of the first to recognize the prevalence and variation in the expression of self-incompatibility (which he termed self-sterility) in flowering plants, he rejected the notion that it had evolved to prevent self-fertilization and its harmful consequences, a role that is now generally accepted. In Forms of Flowers, Darwin often used group selection arguments, such as when discussing optimal sex ratios in dioecious populations (p. 282), and he considered seed set (maternal fitness) as the sole target of fertility selection (pp. 260, 304, 345, 338). It was not until a century later that most workers in reproductive biology abandoned group selection thinking, came to appreciate that plants have both maternal and paternal fitness, and recognized that sexual selection plays a role in floral adaptation … Although Darwin failed to appreciate the importance of sexual selection and male fertility in plants, it is impressive that so much of what he wrote in his three books on plant reproductive biology has proven to be generally correct. It is also intriguing how close Darwin came in his work on heterostylous plants to obtaining the progeny ratios that enabled Gregor Mendel to first establish the principles of inheritance and initiate the science of genetics. The double crown was just beyond Darwin’s reach” (Barrett).

“Much of the content of this [book] had previously been published in the Journal of the Linnean Society of London and elsewhere. Had Darwin not chosen such genetically complex examples, he might have approached more nearly to an understanding of the laws of particulate inheritance. Like Cross and Self-fertilisation, it was too technical a work to command a large sale, and only about 2,000 copies were sold in Darwin’s lifetime, and perhaps 4,000 before the end of the century” (Freeman).



8vo (189 x 126 mm), pp. viii, 352, plus 32 pages publisher’s advertisements dated March, 1877, with 15 woodcuts and 38 tables in text, entirely unopened. Original blind-stamped cloth. Very fine.

Item #5511

Price: $3,500.00

See all items in Chemistry, Medicine, Biology
See all items by