semillas la vida en cápsulas de tiempo - Clh.es

SEEDS – TIME CAPSULES OF LIFERO B K E S S E L E R & M A D E L I N E H A R L E YTIME CAPSULES OF LIFEROB KESSELER & MADELINE HARLEYThere is a magical appeal, rooted in childhood, in watching seeds develop: the acorn in its neatly fitting cup orthe polished, rich brown surface of the horse chestnut as it emerges from its spiny shell. These sensuous formsdraw us closer to nature: temporal touchstones rolled between fingers, stuffed into pockets or left to slowly shrivelon windowsills. Then there is the poppy, with its flame red petals that quickly fall as the fruit ripens into itsfamiliar capsule, the crop of seeds trapped inside, rattling like miniature maracas until the cap lifts and they areeventually dispersed.Holding a small seed in one’s hand it is sometimes difficult to comprehend that given the right conditionsa complex and beautiful plant will emerge from it. Seeds are the begin-ning and end of the life cycle of plants,carriers of the genetic codes that will ensure success-ful propagation and continuation of the species. Theirresilience is renowned: seeds taken from dried herbarium samples have been successfully germinated over twohundred years after they were collected. Their diversity of form and scale is as extensive as the plants from whichthey derive, from the giant coco de mer weighing up to twenty kilos to the almost dust-like seeds of the orchidfamily where one gram can contain more than 2 million seeds.Until the seventeenth century the study of plants had largely been for medicinal or hor-ticultural purposes,but taking advantage of the new compound microscope developed by chemist and physicist Robert Hooke,pioneering botanists such as Nehemiah Grew and John Ray were among the first to describe the structure andreproductive mechanisms of seeds. Fuelled with this new knowledge, a new breed of explorers and plant hunterswere bringing back to Europe exotic flowers and plants to be cultivated by a growing number of botanists andplantsmen. This fuelled a competitive passion for growing flowering plants and subsequently for the gardens inwhich to display them, leading to a demand for ever more exotic varieties to fill the burgeoning hothouses andgardens of the nobility.This growing passion laid the foundation for a more systematic approach to the collec-tion and scientificstudy of plants with the creation of Botanic Gardens. In addition to living plants that miraculously survived thetrials of being transported thousands of miles across land and sea, increasingly the collecting and trading of seedsbecame more commonplace. Today this has evolved into a multimillion pound industry to satisfy the demandsof a highly educated population of garden enthusiasts. But more importantly, as environmental con-cerns havegrown and the importance of the preservation of plant habitats for bio-diversity has been recognised, a networkof highly trained seed collectors with local knowledge of endangered species has emerged. Their precious harvestis distributed among the many centres for botanical research around the world. In recognition of the urgent needfor a concerted approach, the Royal Botanic Gardens, Kew, created the Millennium Seed Bank at WakehurstPlace in Sussex in 2000. The Millennium Seed Bank Project has set itself the daunting but vital task of collectingand conserving by 2010 over 24,000 species – of the world’s seed-bearing flora.In the eighteenth century, artists and scientists worked closely together to examine and portray the manycomplexities of life. In a revival of this collaborative spirit this book reunites the worlds of botanical science andart to reveal and celebrate the astounding diversity and complexity of seeds. As we worked together we marvelledover the specimens in front of us and through our collaboration we hope to show you things you may have seenbut never had the opportunity to examine in minute detail. In the natural world seeds are dispersed on the wind,carried on the backs of animals or eaten by birds and other animals to be deposited far from the original plant.They are dispersed by humans too – as food trans-ported across vast distances, as decorative items of jewellery,or accidentally when stuck to clothing. Through this book we hope to extend the strategy of dispersal to a newaudiencesWHAT IS A SEED?WOLFGANG STUPPYSeeds are time capsules, vessels travelling through time and space. In the right place at the right time each seedgives rise to a new plant. They are the most sophisticated means of propagation created by the evolution of plantson our planet and the most complex structure a plant produces in its life. Seeds have two principal functions:reproduction and dispersal. For most plants, the seed is the only phase in its life when it can travel. Each individualseed carries the potential of the whole plant and even of the species. Tiny herbs and giant trees both grow fromseed. To maximise their success and to fill every available niche, plants have developed an incredible range of seedsizes, shapes and colours. For example, the largest seed in the world (in fact a single-seeded fruit), the Seychellesnut, coco de mer or double coconut, can be 50cm in length, nearly a metre in circumference and weighs up totwenty kilos. The smallest seeds are found in orchids. They can be as small as 0.11mm long and weigh less than0.5µg (= 0.0000005g), which means that one gram may contain more than two million seeds.This amazing diversity, of which the tiniest examples are often of breathtaking beauty and exquisitesophistication, is largely the result of the pursuit of different strategies of dispersal. For a plant it is very importantto find a way to disperse its seeds. This task can be accomplished either by the plant itself through explodingfruits that eject the seeds (the fruits of some legumes catapult their seeds as far as 60m) or by developing a rangeof astonishing adaptations that allow the seed to use wind, water or animals as transport vehicles. By enabling itsoffspring to travel away from the mother plant, even if for a short distance only, a species can conquer newterritories, increase its numbers and alleviate competition between siblings and parents.Imagine that children are being sent away to start a new life somewhere else, perhaps far away. What wouldthey be given to make sure they stand a good chance of survival? They would certainly need something to eat, apacked lunch perhaps. They would probably also be given some kind of protection against the elements and, ofcourse, against predators in search of the tasty morsel they are carrying. This is precisely the strategy of plants. A seedconsists of three basic components: the offspring in the form of a small plant called the embryo; the energy-rich,nutritive tissue surrounding it, called the endosperm; and a protective layer around the outside, usually the seed coat.It is this nutritive tissue, the food reserve of seeds, which makes them so precious, so indispensable for mosthuman societies. It is no exaggeration that our entire civilisation is built on seeds. Think of cereals such as rice,wheat, maize, barley, rye, oat and millet; and pulses such as beans, peas and lentils. They are the main source ofnourishment for billions of people worldwide and they are all seeds. Rice alone is the staple of half the peopleon Earth. Then there are the pleasures in life to which seeds contribute like the nuts we nibble, the beer we drink,or the coffee we crave in the mornings. Seeds provide many of the spices used in cooking: pepper, nutmeg,cumin, caraway, fennel and mustard, to name but a few. Seeds also yield precious raw materials: they providevaluable oils, like the linseed oil used in varnishes and paints; the rapeseed oil that serves as fuel; and castor oil,an excellent lubricant for jet engines and heavy machinery. Another raw material of great economic importanceis cotton, which consists of the hairs shaved off the seeds of the cotton plant.In addition to their immense usefulness, seeds can be extraordinarily beautiful. This book will change forever the perceptions of those who have never appreciated their beauty.Seed evolutionIt is easy to comprehend the basic structure of seeds but few are aware of their underlying complexity. Plantsneeded many millions of years to develop this most sophisticated means of sexual reproduction but it became ahuge success. In fact, the evolution of seed plants from their primitive fern-like ancestors is a key chapter in thehistory of life on Earth. Understanding how and why seeds evolved, and how they have changed the face of ourplanet, makes the journey into the microscopic world of seeds both illuminating and exciting.Where do seeds come from, why do they exist, and what makes them one of the greatest achievements ofplant evolution? In order to answer these questions we have to take a brief look at the evolution of the life cyclesof plants, and, most importantly, their methods of sexual reproduction. Primitive land plants such as mosses(including liverworts and hornworts), clubmosses, horsetails and ferns, the so-called cryptogams, neither haveflowers 1 nor do they have the ability to produce seeds. They reproduce through spores.Seeds and spores could hardly appear more different; for a long time it was believed that they have nothingin common. But in 1851, the self-taught German botanist Wilhelm Hof-meister (1822-77) made a famousEnglish texts 265