From The Great Naturalists edited by Robert Huxley

Born on the island of Lesbos around 372 BC, Theophrastus became acquainted with Aristotle, whom he joined at the Lyceum in 335 BC. After Aristotle's death, Theophrastus took over as head of the school, and remained there for more than three decades. In his heyday, Theophrastus could attract an audience of some 2,000 to hear his lectures. Among other things, he lectured about leaves.

Many of his contemporaries had always thought of cultivated plants as gifts from the gods, bestowed upon humans when the gods were in jovial or generous moods. Their main concerns were maximizing plants' usefulness to people. In that society, Theophrastus did something more important than seek answers; he asked different kinds of questions. Specifically, he aimed to untangle the relationships plants had to each other, without necessarily worrying about plants' usefulness to us. In this mission, he developed four categories for plants: trees, shrubs, sub-shrubs and herbs. Further, he reasoned that leaves could very in form while still retaining some constant characteristics within species.

These observations of leaves and categorizations of plants may sound like small achievements, but we view Theophrastus through a prism of modernity when such categories have long been taken for granted. In his day, the concepts were unknown. So was the concept of pollination, which Theophrastus didn't quite grasp, but he did understand that "it is helpful to bring the male to the female."

One obstacle Theophrastus had to overcome in understanding plants involved scholars' tendency of the time to equate plants with animals. While no one would insist that a woman's baby was still a part of her body, scholars puzzled over how to characterize a plant's fruit. Was it still a part of the plant or not? What about its leaves and its flowers? All these things started out as part of the plant, but eventually came off.

Theophrastus eventually familiarized himself with several hundred species of plants. Compared to the hundreds of thousands of plant species known today, that's a tiny sample. Yet for a man who lived when plants were useful in cultivation (or poison) and otherwise of no interest, it was a remarkable achievement. His Enquiry into Plants and On the Causes of Plants — both of which took up several volumes — likely comprised antiquity's greatest contributions to botany.

Theophrastus's expertise wasn't limited to plants. He also composed a short work titled Concerning Stones. Modern scholars suspect that this was part of a larger work, perhaps lecture notes. The work didn't address minerals, which Theophrastus said he addressed elsewhere (presumably in a work now lost). As in plants, he designated some stones as male and female, likely related to the attraction and repulsion found in magnets. The work mentioned marble, alabaster, gypsum, lapis, coral, and pearls, among others. It also discussed the role of heat and fire in transforming certain stones, such as marble into quicklime.

And in his work on stones, Theophrastus wrote of "dug up" ivory, suggesting that he grasped that fossils might have an organic origin. He also wrote about the petrified forest on the island of Lesbos. So he was probably ahead of Aristotle in understanding fossilization.

Theophrastus agreed with Aristotle on many topics, but for all their close collaboration, Theophrastus questioned some Aristotelian ideas, including whether everything in the universe served an identifiable purpose, and whether fire (as in earth, air, wind and fire) was really an element. Theophrastus's temperament differed from Aristotle's; Theophrastus was less argumentative, less driven by theory and more empirical.

In the centuries following his death, Theophrastus was largely forgotten, his work subsumed in the encyclopedic works of Pliny the Elder. During the Renaissance, his reputation enjoyed a new life, and John Gerard's 17th-century Herball featured an engraving of the ancient scholar on the title page (shown above).

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