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430 In his epoch-making Elements of Systematic Botany, Schleiden, near the middle of the century, challenged the systematists in these words: "The time has passed wherein a man who could give the names of 6,000 plants would because of that be called a botanist, but another who knew 10,000 plants would be designated a greater botanist, and the formerly so-called systematic botany has been thrust back into its proper place of simply a hand servant of the true and exact sciences." But the systematists returned the thrust. One of her foremost representatives declared to the men of the "true science:" "If one were to collect all the positive results thus far offered by plant physiologists it would scarcely suffice to fill a nutshell." Wrong judgments lay here on both sides, such as are always called forth by insufficient knowledge and limited insight into the relation of things. The principle of the division of labor led here, as usual, first to a separation of two so closely related territories, and it was only as one of the later results of the application of this principle that they were again brought into their natural relations.

The science, however, incurred no lasting injury from the fact that descriptive botany and physiology first pursued opposite ways. In each field good constructive material was accumulated. An earlier commencement of common constructive work would only have led to complications.

A really gratifying prospect is presented when one considers how gradually systematic botany was advanced by this branch of physiology in its widest sense. Linnæus and his school could still content themselves with a very elementary form of plant description, form and position of leaves, number and arrangement of flower parts—in short, any character which a plant in flower presented to the naked eye sufficed for the end of plant description as then pursued. Now, however, a hundred thousand species of plants are known. Of orchids alone there are as many species as all the species of plants described by Linnæus put together, and it is easy to see how the few superficial characters at first used for distinction of species became wholly inadequate. Besides, descriptive botany could not content itself with simply distinguishing plant species and supplying them names.

Furthermore, it became necessary to consider the systematic arrangement of the ever-increasing species. There had also to come into play that great principle of natural science investigation which one of our most distinguished colleagues has called the "economy of science." When I speak of orchids I express the sum of all those characters which are common to these 8,000 species. This expression of the sum of common characters must possess this quality, that by it I can distinguish this plant group from all others and, besides, express their relationship to other groups. The sum total of isolated characteristics must be brought into the simplest, briefest expression possible. Linnæus sought to attain this "economy" by his artificial system. This