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An orchard invisible. A natural history of seeds.
J Silvertown. 2009.
London: The University of Chicago Press. $25.00 (hardback). 224 pp.
The publisher's notes and the extracts from two US reviews on the outer jacket suggest that, on the subject of seed, this book will entertain the reader and provide scientific insight. There are nuggets of fascinating information and evolutionary tales, and genuinely amusing quotations and turns of phrase but, for this reader, the book does not entirely meet expectations.
The author refers to the story of the seed as a tale of evolution, but this does not always appear as a convincing theme. He admits that he followed a meandering path and has gone off at times in unexpected directions. As he puts it, ‘like the root of the seedling, I branched into particularly fertile territory whenever I encountered it’, which might be too contrived a simile for some. The author himself makes the point, ‘This is not a long book (who has time for those these days?)’. This encouragement to a casual and easy read does not always match up to the content and style.
The book title ‘An orchard invisible’ followed by the more informative sub-title ‘A natural history of seeds’ sets the style. Each chapter begins with a quotation from which the main chapter heading is drawn, followed by a one word sub-title that tells you more about what is to come After an introductory chapter subtitled ‘Seeds’ there are sixteen further chapters.
The second chapter on evolution takes plants from a marine environment onto land as mosses and ferns, and then on to the gymnosperms, now represented by Ginkgo biloba, cycads and conifers, and finally to the angiosperms, the flowering plants with seeds contained in an ovary. The chapter contains much speculation about the evolution of the endosperm in the seed but understanding may not be helped by the humanizing of the evolutionary process in terms of the interests of mother and father; however, it is a bold attempt to entertain. The reader may also find that the meanderings into herbal medicine and the 16th century use of fern ‘seed’ interrupt the logical flow of the argument.
Chapter 3 on sex is frustrating. There is much literary quotation and historical background but the reader is not left with a clear impression of what the writer wants us to grasp as an insight into the significance of sex to seeds. There is no clear statement of the role of sex in the generation of variability. The nearest we come to this is two chapters later on ‘Inheritance’, in the comment on McLintock's discovery of transposons ‘…that some genes do not follow the choreography of chromosomes segregating in Mendelian fashion to give predictable ratios’.
‘Pollination’ (Chapter 4) begins with Sherlock Holmes' view of flowers as purposeless and then moves to Darwin's experiments that show that the purpose of flowers is to facilitate cross-fertilization. The yucca plant and figs are featured to illustrate the complex co-evolution between plants and their pollinating insect.
The chapter with the one word sub-title ‘Size’ is short and focussed on one species from two small islands in the Seychelles, the coco de mer palm (Lodoicea maldivica). This evolutionary curiosity is used to illustrate that the extreme size results from natural selection. The large food reserves provide nutrition for the development of what the author describes as ‘an umbilical cord’ that grows from the seed to eventually establish the seedling up to 10 m away from the parent plant. The next chapter (‘Number’) is again short and narrowly focussed on one species, the oak tree, and the ‘mast’ years when large numbers of acorns are produced. The author describes one result of this in rural New England. The white-footed mice population, which feeds on the acorns, booms in the year following the ‘mast’. The mice provide a reservoir of infection of a bacterium that is transmitted, by way of the black-legged deer tick, from mice to deer and also to people. In people, the bacterium (Borellia burgdorfrei) causes the debilitating Lyme disease. This story typifies many in the book. An evolutionary outcome involving interactions between seeds of plants with a range of organisms, including humans.
The last four chapters relate to the use of seeds by humans, with specific chapters on ‘Oil’, ‘Beer’, ‘Coffee’ and ‘Gastronomy’. Much of the ‘Oil’ chapter is devoted to sunflower and its North American origin. The chemical structure of plant oils, in particular the distinction between low- and high-saturated fatty acid chains, is explained in an accessible way. This leads on to a description of research showing an association between seeds with a higher proportion of unsaturated oils, which behave like liquids at the molecular level, and the ability to germinate at low temperatures.
The chapter headed ‘Beer’ starts with the domestication of barley in the Middle East and ends with the unravelling of the evolution of the yeasts used in fermentation. The presentation of both the biological and cultural evolution of coffee is a fine example of the author's intention to set seeds in a context that engages interest. He traces Coffea arabica from Ethiopia, through the Yemen to Arab, and later European and American, coffee houses. He points out that some of these coffee houses were the origins of many of the commercial and scientific institutions we know today, for example, the stock exchange in Wall Street and the Royal Society of London. Starbucks gets a mention, as do baseball and the Yankee Stadium, which suggests a tilt to a US readership that is seen elsewhere in the book.
The author does not seek to write a broadly based treatise with arguments supporting a strong evolutionary theme. Rather, he focuses on particular, sometimes peculiar, evolutionary outcomes in seeds that result from the interactions of seed-bearing plants with insects, birds and primates, including humans. His clear and stated intent is to arouse interest and awareness.
The book is not quite what it seems at first. The many quotations and author asides do not lead to a flowing narrative and an easy read. The writing style is familiar with many human analogies. This does not always mean that the text is readily accessible to readers who have no grasp of the basics of genetics and evolution. The book will be enjoyed by readers who have an interest in the natural world and give it a thoughtful read and might, as the author hopes, go on to make use of the 28 pages of sources and suggestions for further reading.