ARISTOTLE'S BIOLOGY parts; wherefore we should regard them not for what they are but for what they are about to be." " Theophrastus realizes the intricate com- plexity of his subject and that a true classifi- cation of plants is beyond him: " In fact your plant is a thing various and manifold, and so it is difficult to describe in general terms; in proof whereof we have the fact that we can- not here seize on any universal character which is common to all, as a mouth and a stomach are common to all animals. . . . For not all plants have root, stem, branch, twig, leaf, flower or fruit, or again bark, core, fibres, or veins; for instance, fungi and truffles; and yet these and such like characters belong to a plant's essen- tial nature. However . . . these characters be- long especially to trees, and our classification of characters belongs more particularly to these; and it is right to make these the stand- ard, in treating of the others." '^ With other ancient writers Theophrastus was much intrigued by conceptions of differ- ences of sex between plants. He did not understand the sexual parts of flowers. With reference to palms, he comes nearest to an idea of the process of fertilization, knowing of long-
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