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11836 results in Plant sciences

Page 52 of 592

  • 19 - The taxonomic challenge ahead

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 439-448

  • Summary

    We live in a species-rich world that is increasingly under human influence. As we have seen in earlier chapters, there is abundant evidence that many species are endangered, and this includes unknown organisms that have yet to be named and classified. If we are to appreciate the true extent of biodiversity, there is a formidable and urgent taxonomic task ahead (Mallet & Willmott, 2003; Bateman, 2011).

    What are the prospects of the completion of a catalogue of life?

    The challenges are discussed by Wheeler (2008), who comes to the conclusion that, at the very point in history where a major effort is required of taxonomists, there is a growing concern that taxonomy has suffered a ‘decline in prestige and support’.

    As we have seen in earlier chapters, taxonomy has a very long history. Wheeler considers that two twentieth-century developments, in particular, have challenged the status, funding and prospects of taxonomic studies. We have seen in earlier chapters that, in the 1920s and 1930s, biologists became increasingly interested in experimental and genetic investigations of evolutionary patterns and processes. Many botanists, initially trained as taxonomists, turned to these investigatory studies to study intraspecific variation, speciation etc. These approaches became known as Experimental Taxonomy or Biosystematics. Huxley (1940) in his classic book New Systematics hoped for the rise of an integrated subject, but Wheeler points out that some biologists, enthusiastic for the emerging specialisms, came to believe that taxonomy, being ‘non-experimental’, was not really a science, but was involved with ‘subjectively naming and classifying species’. Thus, ‘taxonomy involved arbitrary bookkeeping and pigeonholing practices and legalistic wrangling over scientific names, while systematics was experimental and intellectually exciting and expansive’. In parenthesis, we may note that this perception of taxonomy, as ‘merely descriptive’ and ‘non-analytical’, has been very strongly challenged. For example, Lipscombe, Platnick & Wheeler (2003) and Sluys (2013) argue very effectively that taxonomic study is ‘hypothesis driven’.

    Returning to Wheeler's analysis, he points to an even bigger revolution later in the century, when molecular and computational techniques were introduced to energise an already vigorous experimental tradition, providing the tools for major advances in all aspects of micro- and macro-evolution, and the emergence of molecular phylogenetics and modern biogeography.

  • 8 - Intraspecific variation and the ecotype concept

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 135-159

  • Summary

    We saw in Chapter 7 how different breeding systems can be expected to produce different patterns of variation. If we are to understand the variation patterns actually found in nature and the processes that give rise to these patterns, we must discover how the potential variation in seeds relates to the variation of reproductively mature plants. Historically, the first advances in this field were made by means of comparisons between plants belonging to the same species but from different populations. Taxonomists, biometricians and, later, geneticists became interested in genetic variation in the wild, and many of their studies converged at one point, namely, the controversy over the ‘reality’ of the intraspecific groups, which could be distinguished in nature, and whether they were the subspecies or varieties of the taxonomist or the ‘local races’ of the biometrician. A new look at this old question was provided by the famous researches of Turesson published in the early 1920s.

    Turesson's pioneer studies and other experiments

    At the time of Turesson's experiments, the question of the reality of ‘local races’ was combined with another controversial issue, namely how much of the observed variation in natural populations was the result of the direct modification of plants subjected to severe environmental stresses. By the end of the nineteenth century, many botanists reasoned that distinctive intraspecific variants were merely ‘habitat modifications’. Turesson, however, pointed out that in all previous cases known to him, only a partial test of the ‘habitat modification’ hypothesis had been carried out. For example, he considered the studies of Lathyrus japonicus (L. maritimus) undertaken by Schmidt (1899). Baltic populations of this plant have dorsiventral leaves, whilst on the North Sea coast of Denmark the plant has isolateral leaves. Schmidt showed, by experiment, that watering the Baltic variant with sodium chloride solutions induced a leaf structure typical of Danish plants. Given that the North Sea has a higher percentage content of salt than Baltic waters, Schmidt deduced that the leaf structure of the plants on the North Sea coast of Denmark was merely a habitat modification.

    The logic of this type of deduction did not satisfy Turesson. His approach to the problem was to grow samples of several variants of a species in a standard garden, to see if ‘distinctiveness’ was retained or lost.

  • 15 - The species concept

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 331-335

  • Summary

    The ‘species concept’ in biology, as we saw in Chapter 2, has engaged the attention of most of the famous naturalists in earlier centuries, from Ray through Linnaeus to Darwin himself, and debate, argument and controversy continues to the present day (see Rieseberg, Wood & Baack, 2006; Wilkins, 2009; Mischler, 2010; Kunz, 2012).

    Species as part of natural classifications

    Kinds of organisms can be arranged in a hierarchy, each higher group containing one or more members of a lower group. A study of primitive biological classifications reveals that hierarchical classifications are a widespread feature of languages in general, and the particular hierarchy of genus and species, which modern biology uses, is really only a special case of a general linguistic phenomenon. The inescapable conclusion from such comparative studies is that hierarchical taxonomic classifications arise in human societies wherever they develop, and that the detail of the treatment found in folk taxonomies reflects the importance of the organisms concerned in the life of the particular tribe or culture. This view of taxonomy as the product of the human need to understand, describe and use the plants and animals applies to the Latin biological classification we use today.

    Although we talk of associating species into genera and genera into families, that is not what happened in the early days of biological classification. It is indeed arguable that the idea of a kind of plant or animal envisaged by the ordinary person corresponds, in the history of classification, more closely to the modern genus than it does to species. It was these classical and medieval ideas of ‘kinds’ of plants that were available in the eighteenth century to Linnaeus, who stabilised the scientific names in the binomial form in which we still use them. So the Linnaean names (e.g. Quercus = Oak and Fraxinus = Ash) indicate the level of recognition of ‘kinds’ in the botany of medieval Europe. This is beautifully illustrated by the Carrot family (Apiaceae/Umbelliferae), many of which were familiar plants in classical times in Europe, mainly because they were cultivated for food or flavouring (e.g. Daucus = Carrot, Pastinaca = Parsnip) or because they were poisonous (e.g. Conium = Hemlock). All these familiar European plants were accurately described and given what later became their generic names, long before Linnaeus.

  • 11 - Populations: origins and extinctions

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 216-241

  • Summary

    Populations do not exist in isolation: they owe their origin to pre-existing populations. Thus, populations establish, flourish, languish, decline and revive, and finally, for all manner of reasons, become extinct (Harper, 1977).

    Metapopulations

    A family of metapopulation models linking all these stages has proved important in the study of animal populations – from kangaroo rats to monk seals, from mountain sheep to butterflies. The concept has also influenced the study of plants.

    Models take as their starting point that species occur in patches. At any one time some but not all suitable patches are likely to be occupied. Unoccupied patches are colonised by dispersal of seeds or fruits from an occupied patch. In time, while populations in newly occupied sites may expand, eventually numbers may decline and the population becomes extinct. Each population, therefore, has a finite life. Thus, the success of the species regionally will depend upon there being healthy colonies from which recolonisation can repopulate empty patches, where the species has become extinct. Brussard (1997) describes three different types. (i) ‘Classical metapopulations consist of several small extinction-prone local populations connected by a moderate amount of migration’. (ii) Mainland populations or large habitat blocks that supply colonists to small outlying island populations, including islands of land in the sea or lakes; ‘island’ water bodies scattered across a landscape; and isolated mountain tops in a lowland plain etc. (iii) Metapopulation systems may also consist of populations that ‘are declining to extinction because dispersal is too infrequent’ or does not occur to facilitate re-establishment.

    The metapopulation concept has been employed in interpreting patterns of behaviour in plant populations. For example, Pedicularis furbishiae has been studied at sites along the banks of the St John River in Maine, USA. A total of 28 colonies were mapped over a four-year period, and the patterns of colonisation/extinction were consistent with the metapopulation model (Menges, 1990, 1991).

    In another case study employing metapopulation models, populations of the short-lived perennial species Silene latifolia (S. alba) were examined over a number of years in roadside habitats in Virginia, USA (see Altizer, Thrall & Antonovics 1998; Thrall et al., 1998). Overall, 7500 habitat patches were detected, of which some 400–500 were occupied in any one year.

  • 5 - Post-Darwinian ideas about evolution

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 67-73

  • Summary

    For forty years after the publication of the Origin, Darwin's ideas were a source of tremendous public controversy. For this reason he never received any awards from the state, although he was awarded honorary degrees and decorations in plenty. Despite thousands of critical sermons, many accepted Darwin's views on evolution, but, as seen in this chapter, the concept of natural selection was not generally accepted, until the rise of genetics in the mid-twentieth century. The biological literature of the period is full of papers speculating about the adaptive significance of various structures, the probable course of evolution in the plant and animal kingdoms, and so-called ‘evolutionary trees’ showing phylogenetic relationships (Fig. 5.1).

    Some of this work is of lasting interest, but there was a depressing tendency in the later years of the period for armchair biologists to produce highly speculative theories, and there was a lack of critical experiment with living material. Towards the end of the century, however, there were signs of an increasing interest in the possibility of using experiments for the investigation of evolutionary problems.

    Experimental investigation of evolution

    A good example of this change in climate is provided by the controversy that enlivened the pages of Nature and the editorials of The Gardeners’ Chronicle in 1895. At a discussion meeting of the Royal Society, the Director of the Royal Botanic Gardens, Kew, W. T. Thiselton-Dyer, had shown specimens of the ‘feral’ type and cultivated variants of what he called Cineraria cruenta (now called Pericallis cruenta) – the gardener's Cineraria – and an extended account of his ideas was printed in Nature (1895). He suggested, as befitted an ardent and orthodox disciple of Darwin, that, as far as was known, the garden Cineraria was derived from Senecio (Cineraria) cruentus from the Canary Islands ‘by the accumulation of small differences’. Bateson (1895a, b) responded to this view in a lengthy letter to the editor, questioning the assertions of Thiselton-Dyer. Bateson concluded, after a study of the literature, that modern Cinerarias arose from hybridisation between several distinct species, that selection was practised on variable hybrid progeny, and that ‘sports’ may have been important, as well as subsequent improvements as a consequence of the selection of small-scale variation.

  • 14 - Abrupt speciation

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 287-330

  • Summary

    The processes of allopatric speciation discussed in Chapter 13 ‘may be responsible for many, if not most, speciation events’ (Soltis & Soltis, 2009). However, new species also arise abruptly in a sympatric context, often as a consequence of species hybridisation, the ‘evolutionary signature’ of which is ‘rampant’ in many groups of plants (Soltis & Soltis, 2009). In this chapter, our account will reflect the major change of outlook that has emerged in the study of abrupt speciation processes. For example, Stebbins (1971) considered that ‘polyploidy has contributed little to progressive evolution’. This view has been replaced by a radically different ‘consensus view that polyploidy is a prominent force in plant evolution’ (Wendel & Doyle, 2005).

    Our present understanding of abrupt speciation is explored in three sections:

    1. A. The emergence and testing of key concepts in the study of polypoidy

    2. B. Recent insights into polyploidy from molecular studies

    3. C. Other modes of abrupt speciation

    A. The emergence and testing of key concepts in the study of polypoidy

    For close on 100 years, botanists have been investigating abrupt speciation by polyploidy. Using the techniques available (and fashionable) in different periods, hypotheses about polyploid speciation have been tested. We consider the successes and limitations of the various approaches from cytogenetical and karyological methods (first developed in the nineteenth century), to chemical investigations of the 1960s. In presenting a number of case histories we review the emergence of key concepts and consider how early findings have been tested, confirmed, refined and extended by the use of an increasing range of molecular methods.

    The concept of polyploidy: early cytogenetic studies

    As we saw in Chapter 12, Winge's (1917) hypothesis that fertile derivatives could be derived from sterile hybrids by polyploidy was tested in a number of experimental studies.

    A famous case of allopolyploidy was provided by Primula kewensis, which was discovered amongst seedlings of P. floribunda at Kew in 1899. The proposition that P. kewensis was a hybrid between P. floribunda and P. verticillata was put to the test by making the hybrid experimentally, using P. floribunda as female parent. P. kewensis was morphologically intermediate between the parental stocks and had the same chromosome number 2n = 18 (Digby, 1912; Newton & Pellew, 1929).

  • 7 - Breeding systems

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 98-134

  • Summary

    The study of a range of plants in the wild or on display in a Botanic Garden reveals a bewildering array of floral types. Many books describe in some detail a selection of pollination mechanisms, often discussing in highly technical botanical language the variety of floral structure. Special terms have, quite properly, been devised by botanists to enable them to write concise, accurate plant descriptions. Although the botanical literature reports extensively on the structures involved in reproduction, in our opinion, it does not pay sufficient attention to the variety of breeding systems in plants, systems of which complex structures and pollination mechanisms are only a part.

    We have noted in earlier chapters the role of the internal sources of genetic variation, namely mutation and recombination, and have seen that a vast number of gametic types is theoretically possible as a consequence of these factors. Which gametes are actually brought together to form the zygotes, however, depends, to a great extent, upon the breeding system of the plant concerned.

    In this chapter, as a prelude to our discussions of variation within and between species, we consider three areas:

    1. A. The different breeding systems found in flowering plants.

    2. B. Breeding behaviour discovered in studies of wild populations.

    3. C. The evolution of breeding systems.

    Our account discusses how studies of breeding behaviour have developed, and emphasises that a knowledge of the different breeding systems provides an indispensable framework for understanding the complexities of patterns and processes found in nature.

    A. The different breeding systems found in flowering plants

    There are three basic breeding mechanisms, which we examine in turn.

    Outbreeding

    In many animal groups outbreeding – crossing between different individuals – is rendered likely by sexual differentiation. In higher plants, however, separation of the sexes is the exception. According to Richards (1979), only about 4% of the flowering plants are dioecious. A slightly higher figure is reported by Renner & Ricklefs (1995), who note that c.6% of angiosperm species are dioecious, these species being distributed amongst 7% of genera. The incidence of dioecy varies in different floras. While only c.3% of British flowering plants are dioecious, much larger percentages are reported, for example, from groups of distant oceanic islands such as Hawaii (28%) and New Zealand (13%).

  • 1 - Investigating plant variation and evolution

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 1-3

  • Summary

    The endless variety of different organisms, in their beauty, complexity and diversity, gives to the biological world a special fascination. Some recognition of these different ‘kinds’ of organisms is a feature of all primitive societies, for the very good reason that humans had to know, and to distinguish, the edible from the poisonous plants, or the harmless from the dangerous animal. There is also a further dimension to the variation pattern. From folk taxonomies, the early product of human societies’ need to understand, describe and use the plants and animals around them, the modern scientific biological classifications we use today have been developed. Different ‘kinds’ of organism are arranged in a hierarchy, each higher group containing one or more members of a lower group. We now distinguish more than a quarter of a million flowering plants, and these are arranged in a hierarchical-nested classification of species in genera, genera in families, families in orders etc.

    One of the main issues to be examined in this book concerns the nature of species in this hierarchical system. Anyone familiar with the vegetation of an area, or the plants in a Botanic Garden, has to face a number of questions that have puzzled biologists. Is there any objective way of delimiting species? How can one account for the different degrees of intraspecific variation found in species? Why are certain species clearly distinct, while in other cases we find a galaxy of closely similar species, often difficult to distinguish from each other? Why is it that hybridisation occurs frequently in certain groups of plants and not in others? What is the significance of the hierarchies in classification and what is the origin of these groupings?

    Historically, an examination of these questions, as we shall see in Chapter 2, produced a static picture of variation, based on a belief in the fixity of species. The hierarchy of classification reflected the plan of Special Creation. However, since 1859, with the publication of On the Origin of Species, all such studies have been made in the light of Darwin's profound generalisation of evolution by natural selection: populations and species vary in time and space and are part of a continuing process of evolution.

  • 3 - Early work on biometry

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 23-36

  • Summary

    In the second half of the nineteenth century, as Darwinism was making its impact upon biology, an interesting new approach to biological variation, especially intraspecific variation, was being examined. Instead of trying to describe variation patterns in words, the investigators, examining large samples of organisms, collected numerical data and subjected them to statistical analysis. In the following account we discuss selected themes: for comprehensive studies of the subject see Pearson & Kendall (1970), Kendall & Plackett (1977), Porter (1986) and Stigler (1986).

    The first worker to study natural variation statistically, a science that became known as biometry, was probably the Belgian Quetelet (1796–1874). He wrote a famous series of letters on the subject to his pupil, the Grand Duke of Saxe-Coburg and Gotha. Later in the century, Darwin's cousin, Francis Galton (1822–1911), made notable contributions to the statistical investigation of variation and inheritance, ideas that were developed by many other investigators, especially in relation to social issues (see Bowler, 1989; Keynes, 1993; Gillham, 2001; Bulmer, 2003).

    Biometrics and eugenics

    While Darwin and others considered humankind to be a single species, others, for example the American biologist Louis Agassiz (1807–73), took the view that there were several species of humans. In the developing fields of anthropology and sociology, biometrical methods were increasingly employed to examine racial variation.

    Darwinian concepts provoked many questions with social implications. In 1871, in his book The Descent of Man, Darwin wrote:

    With savages, the weak in body or mind are soon eliminated; and those that survive commonly exhibit a vigorous state of health. We civilized men, on the other hand, do our utmost to check the process of elimination; we build asylums for the imbecile, the maimed, and the sick; we institute poor-laws; and our medical men exert their utmost skill to save the life of every one to the last moment … Thus the weak members of civilised societies propagate their kind. No one who has attended to the breeding of domestic animals will doubt that this must be highly injurious to the race of man.

    (Darwin, 1871)

    Darwin continues:

    The surgeon may harden himself whilst performing an operation, for he knows that he is acting for the good of his patient; but if we were intentionally to neglect the weak and helpless, it could only be for a contingent benefit, with a great and certain present evil.

  • 2 - From Ray to Darwin

  • David Briggs, University of Cambridge, S. Max Walters, University of Cambridge Botanic Garden
  • Book:
    Plant Variation and Evolution
    Published online:
    05 June 2016
    Print publication:
    30 June 2016, pp 4-22

  • Summary

    In 1660 Robert Sharrock, Fellow of New College, Oxford, wrote a book titled History of the Propagation and Improvement of Vegetables by the Concurrence of Art and Nature. He was concerned in its early pages to debate a live issue of the day (Bateson, 1913), namely:

    It is indeed growen to be a great question, whether the transmutation of a species be possible either in the vegetable, Animal or Minerall Kingdome. For the possibility of it in the vegetable; I have heard Mr Bobart and his Son often report it, and proffer to make oath that the Crocus and Gladiolus, as likewise the Leucoium, and Hyacinths by a long standing without replanting have in his garden changed from one kind to the other.

    The Bobarts were both professional botanists. Sharrock investigated their claim, and found ‘diverse bulbs growing as it were on the same stoole, close together, but no bulb half of the one kind, and the other half of the other’. In this age we find it hard to understand a belief in the possibility of transformation of Crocus into Gladiolus. Our reason for disbelief is partly concerned with the nature of evidence; we are not satisfied with the test for the alleged transmutation and would not have been content merely to examine the crowded underground parts. Another reason, however, relates to current ideas of the nature of species. We have a different notion of species from that of the seventeenth century.

    Ray and the definition of species

    It was the English naturalist John Ray (1628–1705) who was probably the first man to seek a scientific definition of species (Raven, 1950; Oswald & Preston, 2011). In his definition is an implied rejection of the sort of transmutation of species claimed by the Bobarts of Oxford, although in other passages in Ray's work he does not wholly dismiss the possibility of transmutation. For instance, he cites as reliable the case of cauliflower seed supplied by a London dealer, which on germination produced cabbage. Richard Baal, who sold the seed, was tried for fraud and ordered by the court at Westminster to refund the purchase money and pay compensation (De Beer, 1964).

  • 18 - Plant Diversity and its Conservation

  • S. L. Kochhar, University of Delhi
  • Book:
    Economic Botany
    Published online:
    08 February 2018
    Print publication:
    24 June 2016, pp 615-626

  • Summary

    The earth supports approximately five to ten million species of plants and animals (IUCN, 1980), which have been the result of three billion years of evolution, including mutation, recombination and natural selection. Humans have been in existence for some two million years. Our prehistoric ancestors were a hunter of animals and gatherer of plants. As compared to the history of man, agriculture is a very recent innovation. It was only about 12 000 years ago that women probably started collecting plants from the wild and began cultivating them, leading to the birth of agriculture. For its continued growth, however, we have to protect the basic life support systems consisting of soil, water, flora and fauna and the atmosphere.

    Walter G. Rosen coined the term biodiversity (or biological diversity) in 1985, and it refers to the variety of life forms and habitats found in a defined area. The Convention on Biological Diversity (CBD) defines biodiversity as ‘variability among living organisms from all sources, including inter alia, terrestrial, marine and other aquatic ecosystems; this includes diversity within species (intraspecific) as well as among species (interspecific) and ecosystems’.

    Plant genetic resources are the most precious but very vulnerable and irreplaceable natural assets of a nation. They have evolved through thousands of years of natural and human selection—both conscious and subconscious. However, certain developments of relatively recent times are posing great threats to the basic life support systems that protect rich plant diversity.

    Threats to Biodiversity

    The chief causes for the disappearance of plant species are as follows:

  • • Destruction of habitats through fragmentation; environmental pollution (such as acid rains, discharge of industrial effluents, increased use of agrochemicals, build-up of greenhouse gases, leading to global warming and the destruction of ozone layer by aerosol sprays and refrigerant fluids); sea pollution (through oil spills, etc.); deforestation; soil erosion (the destruction of top soil, encroachment of deserts); agricultural expansion; overgrazing; urbanisation; forest fires; developmental activities, such as dams, reservoirs, roads, railway lines, cropland; industries; mining, etc.

  • • The introduction of invasive exotic species are known to threaten the survival of many native species, for example, [Chromolaena odorata (L.) King and H.E. Robins (Syn. Eupatorium odoratum L.)], Parthenium hysterophorusL., Eichhornia crassipes (Mast.) Solms., andLantana camara L.-the latter has entered into forests, seriously competing with native species for factors like competition for nutrients, space and habitat.

  • 19 - Petrocrops: Our Future Fuels

  • S. L. Kochhar, University of Delhi
  • Book:
    Economic Botany
    Published online:
    08 February 2018
    Print publication:
    24 June 2016, pp 627-643

  • Summary

    Fuel is one of the mankind's primary necessities, and it is indispensable, both in the home and industry. The use of wood as a fuel for heating and cooking dates from the earliest times. The more popular fossil fuels (principally coal, petroleum, etc.) and even the nuclear fuels (principally uranium, thorium, deuterium, and lithium) would be exhausted over a period of time because of over exploitation. Forests will ultimately remain our last reservoir. However, over the centuries, forest resources have been endangered in a number of ways as a result of man's unrestrained activities such as overgrazing, indiscriminate lumbering, agricultural operations and burning.

    With the depletion of fossil fuel reserves on one side and their ever-increasing demand for our expanding industries and thirdly the threat of global warming through rising levels of greenhouse gas emissions, the world has seen in recent years a paradigm shift over handling the question of our energy needs.The search for viable alternative energy sources has become more urgent than ever before and the countries are turning back to nuclear energy, geothermal, solar power, wind and water power, etc. Another option available for us is to tap the potentials of ‘Energy Crops’ or ’Energy Plantation or plants producing hydrocarbons or utilisation of vegetable oils - both edible or non-edible - although renewable but would they be able to keep in check the carbon dioxide emission level!

    Traditional or Conventional Energy Crops

    As gasoline prices soar and the supplies dwindle, a shift from food production to fuel production (alcohol) has come to be encouraged in many affluent countries. Of all the energy crops, sugarcane (Saccharum officinarum L.) is known to give the highest alcohol yield per hectare. The combination of high alcohol yield coupled with the built-in source of fuel, in the form of bagasse, to operate the distillery, makes sugarcane exceedingly attractive candidate as an energy crop. The ‘energy canes’ developed in Puerto Rico and Cuba not only provide approximately the same amount of sugar per hectare as the standard cane, but also produce about three times more bagasse, making the whole industry self- supporting in energy.

  • 7 - Fruits and Nuts

  • S. L. Kochhar, University of Delhi
  • Book:
    Economic Botany
    Published online:
    08 February 2018
    Print publication:
    24 June 2016, pp 237-296

  • Summary

    Fruits are undoubtedly man's oldest food and must have always been a source of pleasure for him because of their flavour and taste. Their history is perhaps as old as that of Adam, Eve and the forbidden apple. It is stated in the Bible that an apple tree grew in the Garden of Eden and its fruit symbolised knowledge that mankind was not supposed to acquire. Evil came to the world when Eve and Adam ate the forbidden apple. In addition, the Bible says that Adam and Eve used the leaves of fig, growing in the Garden of Eden, for clothing themselves after they had committed sin by eating the forbidden apple.

    In pre-agricultural days, our early ancestors lived on wild game, fruits and succulent herbage. Most of our common fruits have their origin in the parts of the world that were inhabited by the early man. When men took to organised agriculture, they mainly cultivated grain crops and grew some fruit trees in their backyard. It is possible that some fruit plants might have been cultivated even before the cereals and that grape vines, dates and figs were among them. Archaeological findings (desiccated faeces) give definite clues about the primitive diet and the gradual change that occurred with the domestication of plants.The backbone of Mesopotamian agriculture consisted of crop plants that are still important to the world's food supply; wheat and barley, dates and figs, and olive and grapes. In the New World, man had brought under cultivation practically all the indigenous food plants we now use such as maize, potato, tomato, squash, pumpkins, groundnuts, kidney and lima beans, cranberry, avocado, Brazil nut, cashew nut, black walnut, pecan, pineapple, cacao, vanilla, etc. No important fruit plants were common to both hemispheres, the coconut and certain gourds perhaps being exceptions.

    Cultivation of fruits (pomology) is now a highly profitable enterprise. There is a growing realisation amongst people that fruits should no longer be considered a luxury, but a necessity. Like vegetables, they are classed as protective foods', essential for the maintenance of health (see Box 7.1). They are considered to promote health and prevent diseases. Dietitians or nutrition experts everywhere recommend the consumption of at least 5-7 g of fruits in our daily diet in addition to cereals, pulses, milk and vegetables.

  • 2 - Fibres and Fibre Yielding Plants

  • S. L. Kochhar, University of Delhi
  • Book:
    Economic Botany
    Published online:
    08 February 2018
    Print publication:
    24 June 2016, pp 20-63

  • Summary

    Unquestionably, fibre yielding plants are second only to the food plants in their usefulness. Primitive tree dwellers and cavemen lived by hunting and foraging over fruits, seeds and roots that nature provided. Wool and hides provided the first clothing to these predecessors of modern man. Long before recorded history, however, primitive man had turned his attention to plant fibres, not only for tying and thatching but eventually for weaving lighter, cooler and more pliable fabrics than skins and hides.

    Ropes of various kinds have been identified in the Egyptian tombs that are estimated to be nearly 4000 years old. In addition, craftsmen have been shown making ropes in tomb paintings dating from 500 BC. Palm leaf fibres were found among 12000-year-old artifacts during the Tehuacan Valley excavations in Mexico. A beautifully crafted net, made from Apocynum bast fibres, dating as far back as 5000 BC has been discovered in the Danger Caves, Utah, USA. Fragments of woven flax fibres have also been unearthed in the ruins of Swiss lake dwellings, nearly 10000 years old.

    The art of spinning and weaving was founded in the Stone Age. Perhaps the earliest and simplest form of baskets were made by tying together the ends of a number of stout branches of willows (Salix spp.) and then weaving more slender flexible branches in and out until a conical basket was formed. The primitive basketmaker invented many of the stitches or weaves seen in the modern textiles. The knowledge of weaving gained by the basketmaker was further applied in the manufacture of matting or weaving better cloth from finer material discovered with time. As time progressed, finer materials were discovered and the skill perfected, which was later used for weaving better cloth.

    Before weaving fabrics, fibres must be spun into yarn - a continuous twisted thread made up of interlocking fibre strands. Originally, a yarn was prepared entirely by hand. Distaff and spindle were the first hand tools used for spinning purposes, this further led to the invention of a familiar spinning wheel during the Middle Ages. Today's automated power spinning machinery also uses the same principle.

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