“Nature's Magicians
By Jonathan Silvertown
Scribner, 256 pages, $29
'Quietly and unobtrusively," Jonathan Silvertown writes in "Nature's Magicians," leaves "conjure up our world." We may not stop often to appreciate the hidden alchemy of leaves, but in this engaging and revelatory book, Mr. Silvertown gives center stage to the extraordinary, essential leaf, demystifying its evolution, inner workings and irreplaceable role in life on earth.
One reason we take leaves for granted may be their incredible abundance. Most land plants sprout leaves, which include evergreen needles and blades of grass. Mr. Silvertown calculates that at their seasonal high point there are a thousand times more leaves in one type of British grassland than there are stars in the Milky Way galaxy. He archly suggests that we adopt "botanical" instead of "astronomical" to describe mind-bogglingly large numbers.
Without the ubiquitous leaf, life as we know it would not exist. In their leaves, plants create much of the oxygen we breathe and, directly or indirectly, nearly all the food we eat. By removing carbon from the air and locking it away in plant tissues, leaves help cool the planet. And when their work is done, leaves fall to the ground and decompose, creating fertile soil.
Which came first, the plant or the leaf? Why did leaves evolve? Why do they change color in the fall? With approachable prose and a sprig or two of humor, Mr. Silvertown, an evolutionary biologist and honorary professor at the University of Edinburgh, as well as the author of several books of popular biology, has a knack for creating aha moments for the nontechnical reader. Though the topic of "Nature's Magicians" is ostensibly leaves, his book cuts a much wider swath than its nominal subject would suggest.
Plants' "signature trick," the foundation of life on earth, is photosynthesis, which converts light energy into chemical energy. This sleight of hand, Mr. Silvertown explains, was first performed by aquatic bacteria more than three billion years ago. Then about 1.25 billion years ago, one of these photosynthesizing bacteria partnered with another one-celled organism to create green algae, one lineage of which became the ancestor of all plants.
Plants migrated from water to terra firma some 500 million years ago. For the next 50 million years they had no leaves and conducted photosynthesis in their bare stems. Eventually plants trapped so much carbon dioxide, which is necessary for photosynthesis, that CO2 levels in the atmosphere plummeted by 90%. Leaves evolved as bigger, more efficient platforms for capturing the gas.
Mr. Silvertown adeptly describes what happens inside a leaf as it works its photosynthetic magic. Sunlight is absorbed by chlorophyll, a large, complex molecule found in microscopic bodies called chloroplasts, which give plants their green color. Meanwhile, carbon dioxide enters the leaf through tiny openings called stomata. Carbon dioxide and water meet in the chloroplasts, where solar energy breaks down their molecules and reassembles them into the sugar glucose plus "a side order of oxygen," the author writes. The oxygen, a waste product as far as the plant is concerned, is then released into the atmosphere, where it has accumulated for hundreds of millions of years.
After some plants evolved leaves, they began shading out shorter specimens. This launched "an evolutionary race upward toward the light," which eventually produced trees as we know them. Leaves also created the raw material for trees' bark and wood, and even the suction to lift water far from the roots via a network of internal plumbing called xylem. When leaves release water vapor through their stomata, they start the process of evapotranspiration, which draws water up to the tallest part of a plant, like a beverage being sucked through a straw.
Evapotranspiration also helps leaves avoid overheating as they absorb sunlight. More than 90% of the moisture coursing through plants is released into the atmosphere. "More water is transpired through leaves than flows through all the streams and rivers on Earth," Mr. Silvertown writes. "A tree is a river to the sky, carrying water from the soil into the clouds," whence it falls as life-giving rain.
Since leaves are costly in materials and energy, plants sculpt them to withstand wind and coat them with a waxy cuticle to repel water. Some plants infuse their leaves with chemicals that are toxic to pests but useful to humans in moderation, such as the bitter tannins in tea and the fragrant oils in mint and rosemary. Other plants protect their leaves with powerful alkaloids, including stimulants such as nicotine and narcotics such as cocaine.
Eventually, Mr. Silvertown writes, "leaves wear out." Plants are ruthless in shedding those that are damaged or diseased or that they can no longer maintain, for instance during dry weather. Thick, tough evergreen needles are specially adapted to withstand drought and cold, but the thinner, broader leaves of deciduous trees cannot survive such harsh conditions and so go out in a blaze of autumnal glory.
What accounts for this annual spectacle? To recoup some of their considerable investment, plants break down chlorophyll, then draw its chemical components and other nutrients through the stem and into the trunk and roots for later reuse. In the absence of the green chlorophyll, red, yellow and orange pigments protect leaves from sun damage during this delicate recycling. Even so, not all nutrients are recovered, and some of them fall along with the leaves to enrich the soil.
The crucial thing, Mr. Silvertown explains, is that "leaves are cast off with abandon." If they fell only when the plant died, earth's soil would be poor and unproductive. Instead, the soil holds nearly four times as much carbon as all living plants combined. "The death of leaves," he writes, "is one of the many gifts that plants make to the world." Not to worry, a new crop will emerge in the spring, as the ancient magic begins anew.
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Mr. Helferich is the author of "Humboldt's Cosmos: Alexander von Humboldt and the Latin American Journey That Changed the Way We See the World."” [1]
1. REVIEW --- Books: A Leaf Less Ordinary. Helferich, Gerard. Wall Street Journal, Eastern edition; New York, N.Y.. 17 Oct 2026: C9.
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