Out of Nature: Why Drugs from Plants Matter to the Future of Humanity

2. Humans and Plants

28 2 Humans and Plants Bristlecone pine (Pinus longaeva). Humans and Plants 29 one of the most inspiring things about plants is their individuality . Each species has its own distinct set of features, such as a flower unique in scent or color or a fruit distinct in taste. Even the same plant—a tree in the front yard or a shrub by the window—is never quite the same from year to year. The often cyclical and predictable lives of plants—the breaking of buds, the blooming of flowers, the falling of leaves—remind us that nature is not static. Constant change defines nature, whether that change is growth, death, or adaptation . The emergence of a tiny garden plant from the turmoil of earth brings hope. A human hand planted the seed, a human tended the soil, and so a human is in one way or another connected to this plant. Our relationship with plants is complex, both collectively as a species and individually as people, and in our modern world, understanding and defining this relationship have become increasingly challenging. Trees, the most noble members of the plant kingdom, are symbols of strength and wisdom. They are living history, built upon trunks that tell the stories of their lives. For some trees, such as bristlecone pines, these stories may be very long, with thousands of chapters, one for each year of a tree’s life. One of the oldest bristlecones, an individual of the species Pinus longaeva, is nearly 5,000 years old. This particular tree is so ancient that it has been named Methuselah. Methuselah the tree, however, has lived almost five times longer than his biblical counterpart of the same name, and his home is located in an undisclosed area in the White Mountains of California. The tree has experienced the greater part of an era in the Pacific coast’s history marked by human habitation, from the first native tribes to occupy the land to the pressing expansion of modern cities. There are trees in the Americas that have seen Christopher Columbus come and go and that live to tell us, in the patterns of their rings, what the weather was like and how old they were when the admiral disembarked from the Niña. A tree’s growth rings tell us when life was good, when it was able to grow quickly and set down a new, thick layer of xylem, the inner water-conducting tissue of plants that in trees forms the sapwood and the heartwood. The rings tell us, too, when life barely progressed, when basic survival, rather than growing taller and wider, was the primary concern. We can tell, from the patterns, shapes, spacing, and nicks in the rings, if and when factors such as fire, wind, drought, and even infestation with insect larvae 30 out of nature influenced a tree’s life. In this way, trees are portals to long-forgotten eras in the history of both humans and the environment. Deciduous trees remind us that Earth works in cycles. The shading of leaves from green to yellow and red in autumn tells us that winter is right around the corner. The cyclical patterns that characterize Bristlecone pines are some of Earth’s longest-lived species. The Rocky Mountain bristlecone pine, Pinus aristata, is shown. (Photo credit: Jeremy D. Rogers) Humans and Plants 31 the lives of plants have been repeated year after year ever since the first vascular plants appeared on Earth, more than 410 million years ago. And each year since modern society developed in the United States, complete with trains and automobiles, the onset of fall colors in northern regions has served as a famous attraction, drawing visitors from all over the country and the world. In the United States, the changing of the leaves is such a popular event that the Forest Service maintains a phone hotline for information on “fall foliage hotspots”— the national forests that are the most popular for viewing fall colors. Of course, the phenomenon of fall colors extends far beyond North America, to wherever deciduous trees grow, and in many of these places, leaf-peeping tourists are an annual economic boon. At its most fundamental level, the changing of leaf color is a process of senescence and heralds the onset of winter dormancy. In woody plants, in the final days before leaf fall, an abscission layer forms at the base of the petiole, or the stalk of the leaf. This layer enables a...