INTRODUCTION 207
therapeutics and diseases, with a wealth of solid information that has hardly ever been utilized by our science.
It is hoped that these researches will chiefly appeal to botanists and to students of human civilization; but, as it can hardly be expected that the individual botanist will be equally interested in the history of every plant here presented, each subject is treated as a unit and as an independent essay, so that any one, according to his inclination and choice, may approach any chapter he desires. Repetitions have therefore not been shunned, and cross-references are liberally interspersed; it should be borne in mind, however, that my object is not to outline merely the history of this or that plant, but what I wish to present is a synthetic and comprehensive picture of a great and unique plant-migration in the sense of a cultural movement, and simultaneously an attempt to determine the Iranian stratum in the structure of Chinese civilization. It is not easy to combine botanical, oriental, philological, and historical knowledge, but no pains have been spared to render justice to both the botanical and the historical side of each problem. All data have been sifted critically, whether they come from Chinese, Japanese, Indian, Persian, Arabic, or classical sources, and in no instance have I depended on a second-hand or dogmatic statement. The various criticisms of A. de Candolle, A. Engler, E. Bretschneider, and other eminent authorities, arise from the critical attitude toward the subject, and merely aim at the furtherance of the cause.
I wish to express my thanks to Dr. Tanaka Tyôzaburb in the Bureau of Plant Industry of the Department of Agriculture, Washington, for having kindly prepared a translation of the notices on the grape-vine and the walnut from Japanese sources, which are appended to the chapters on the history of these plants. The manuscript of this publication was completed in April, 1918.
The generosity of Mrs. T. B. Blackstone and Mr. Charles R. Crane in contributing a fund toward the printing of this volume is gratefully acknowledged.
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