The Wood for the Trees: The Long View of Nature from a Small Wood. Richard Fortey

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СКАЧАТЬ tiny green herb. It is another special plant in the ghost orchid mould lacking all chlorophyll, a spooky spectre, and somehow implausible. It is called the Dutchman’s pipe, or if you prefer, yellow bird’s nest, and by scientists Monotropa hypopitys. I have never met a pipe-smoking Dutchman, but I would now recognise the shape of his favourite accoutrement.

      On my hands and knees, I brush away a few loose leaves concealing the bases of the stems of the new discovery. They look a little like blanched asparagus spears, complete with scattered scales. They are the only plants growing in the deep shade. They really do rise straight out of the ground. I would be willing to bet a hundred squirrel tails that if I dug down they would originate from swollen roots such as Eleanor Vachell found for Epipogium. I am not going to try it. A small beetle emerges from one of the flowers, having, I suppose, helped to fertilise it. Over the next few weeks I keep tabs on the small blooms: they last and last. The Dutchman’s pipe is not taking many risks when it comes to setting seed.

      Monotropa has recently been the focus of botanical research. In my old edition of Keble Martin – and in many later books – it sits all by itself in its own plant family (Monotropaceae). It seems that no expert could quite make up his or her mind where such a weird, penumbral paradox fitted into the grand scheme of plant evolution. In North America a related, almost supernaturally pallid species is known as the Indian, rather than Dutchman’s, pipe, or sometimes as ‘the corpse plant’ (Monotropa uniflora), which suggests that we are never going to be able to escape the whiff of the graveyard in this chapter. When the techniques of molecular analysis to determine ancestry became widely available it was not long before both species of Monotropa were allied with a much larger plant group, the Ericaceae, the familiar heather (or blueberry) family, with something like four thousand species worldwide. The Dutchman’s pipe was, in its essentials, a heather that had lost everything above ground except the flowers. Now that I study them again, the flowers of Monotropa do indeed recall those of strawberry trees, blueberries or bell heathers – perhaps we should have known all along. Occasionally, science just reinforces common sense.

      The root of the ghost puzzle really is the root. All our ghostly plants, whether orchid or pipe, have similar-looking roots, which are tuberous and puffy. Both the loss of chlorophyll and the ability to thrive under the beech canopy are the result of special adaptations secretly hidden away underground. V.S. Summerhayes was right in essence: neither the Dutchman’s pipe nor the ghost orchid manufactures its own nutrients. But he was wrong to assume that these plants were what he termed ‘saprophytes’ – that they sourced all they needed from the rotting leaf litter surrounding them. The explanation is both more complicated and much more wonderful than mere scavenging. Monotropa and Epipogium are playing parasitic piggyback on mushrooms. In the case of the Dutchman’s pipe the fungus has been identified with an ordinary-looking mushroom that has been called the girdled knight (Tricholoma cingulatum)8 – not exactly a regular ‘shop mushroom’, since it has a greyish cap and white gills, but constructed along the same familiar lines. Our pallid plant has given up any attempt to manufacture its own necessities in favour of stealing all it wants from its fungus host. Above ground, it needs to be nothing more than flowers and seeds. Like some Regency dandy feeding off colonial slavery, the organism can be all show and no hard graft. The distinctive roots of the plant reveal the truth: they are full of fungus, and modern techniques of DNA analysis allow the molecular biologist to identify exactly which species from a choice of thousands. When I started out in science as a botanising youth this would have been impossible, but now it is almost routine procedure back in the laboratory.

      However, this is not the end of the story. For the fungus itself lives in an intimate association with beech trees in deep woodland. The ‘roots’ of the fungus are masses of threads called mycelium. These threads move through the moist soil seeking out nutrients, and they are skilled in reprocessing all that mush and drift of rotting leaves. Mycelium is the workhorse of the fungus, while the familiar mushroom fruit body is just the culmination of the life cycle for spreading the minute spores of the species. Like many other fungi, Tricholoma forms a partnership with the roots of beeches, where it can live for many years. The threads of mycelium fully coat the growing tips of the roots rather as tight-fitting kid gloves enclose the fingers, and the fungal talent for acquiring important foodstuffs such as phosphates from the surrounding environment becomes essential for the healthy growth of the tree. The fungus-coated rootlets seek out valuable molecules. The fungal dressing is called mycorrhiza, which is simply a classical way of saying ‘fungus root’. Mycorrhiza makes for a reciprocal partnership, because the tree in its turn does what it does best – manufacturing sugars and other products of photosynthesis – and supplies them to the growing fungus, which cannot make them for itself. It is a symbiosis, an intimate growing-together. Like a well-honed comedy duo, each partner would fall flat without the other.

      So the Dutchman’s pipe is at the foppish apex of a ménage à trois. The beech works with sunshine and rainfall, and supplies the fungal partner on its roots with the means to quest for more exotic vital nourishment. Monotropa is a parasite on the fungus, so indirectly it too benefits from the photosynthetic work of the lofty beeches, and can dispense with its own green parts. The fungus supplies everything else. Freed from the need for light, the parasite can safely flower in deeply shady glades where nothing else can prosper.9

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