These relationships are the central subject of Sheldrake’s book. Life on earth as we know it is rooted—or perhaps I should say entangled—in a roughly 600-million-year-old relationship between plants and fungi. When green algae made its way from the swamps and estuaries that covered much of the earth during this period, it had no means to tap into the nutrients it needed on land. In order to survive, the algae teamed up with fungi in what are now called “mycorrhizal relationships,” which are integral to most plant species, “a more fundamental part of planthood than fruit, flowers, leaves, wood or even roots.” In most cases, both species benefit. Fungi tap into sugars and lipids produced by plants during photosynthesis. Plants gain access to a whole host of minerals and other nutrients consumed by enterprising fungi. As Sheldrake writes, “By partnering, plants gain a prosthetic fungus, and fungi gain a prosthetic plant. Both use the other to extend their reach.”
The photos in the new edition—many of them images scanned with electron microscopes—complement his endeavor, literally giving form to processes that we cannot see with our own eyes. What we typically think of as a mushroom is the fruiting body that appears above ground, but much of the action that leads to this often fleeting moment takes place out of sight, within the dense rootlike structure known as the mycelium. Mycelia, in turn, are made up of countless individual hyhpae, microscopic tube-shaped cells that are responsible for gathering nutrients and water, often in partnership with trees or plants. It is hard to overstate the importance of these underground networks, which make up at least a third of the living mass of soils. “Mycorrhizal mycelium is a sticky living seam that holds soil together,” Sheldrake writes. “Remove the fungi, and the ground washes away.” Some of the most revealing images in the book are those of various kinds of wood-rotting fungi alongside their mycelial networks.
Humans too have long benefited from their use of fungi, most notably with the discovery of penicillin in 1928. (There is evidence that the medicinal properties of penicillin have been understood for far longer, perhaps even before Homo sapiens: One recent study found that Neanderthals, who went extinct roughly 50,000 years ago, made use of penicillin-producing mold.) Fungi have also been deployed in a wide range of pharmaceuticals, including in an immunosuppressant that makes organ transplants possible, in cholesterol-lowering drugs, and in a number of antiviral and anticancer compounds. And mushrooms have proven useful in cleaning up contaminated environments, including oil spills, plastics, and even nuclear waste, in what has been dubbed mycoremediation. (Sheldrake’s mentor, Paul Stamets, wrote a book on the subject in 2005 titled Mycelium Running: How Mushrooms Can Help Save the World.)