Compelling evidence of the need to protect Earth's plant species. The authors describe new medicinal uses for plants (e.g., periwinkle is used for childhood leukemia, and the ancient ginkgo is being tested for treatment of Alzheimer's) and discuss the ""green revolution"": through hybridization and modern agricultural practices, people have come to depend on fewer than three dozen crops for food--out of an estimated 240,000 kinds of plants. This specialization will put the planet in grave danger when, as seems possible, weather conditions change or new diseases appear. Other subjects here include efforts to save the germ-plasm ""gene pool"" through seed banks and tissue-culture programs; and botanists who work with jumping genes, protoplast fusion, gene splicing, etc. Vivid, clearly written, up-to-date, and inspiring, this is science writing at its finest. Photos not seen. Index.