INTRODUCTION

Plants produce a bewildering array of exotic chemicals: the pigments which give color to leaves, petals, fruits, and seeds; the substances that create aromas and tastes; those formed to help defend against attack by diseases, predators, and competitors; and others with no known function (Figure 11).

We take advantage of the munificence of plants as chemical factories in many different ways, most crucially in medicine. Worldwide, at least a quarter of medicines come directly from plants; in some places, much more.

SIGNALING

Plants and animals put a great deal of time and energy into attracting attention to themselves. By way of colors, scents, sounds, vibrations, and elaborate movements, such as those in mating displays, living things send signals to one another. The distances over which these signals are sent may be short (a few centimeters) or long (kilometers in the case of some chemical sex attractants; the male gypsy moth can detect the scent put out by a female over 3 km away!).

Signaling is one of the essentials of life. No plant or animal could afford the cost of giving off “pointless” signals; the energy cost is too great. In The Origin of Species, Charles Darwin put it as well as anyone could in the case of flower color: