The foundation of any course of reading on hybridisation and selection should be Darwin's _Effects of Cross and Self-Fertilisation in the Vegetable Kingdom_, which, with his books _On the Origin of Species by means of Natural Selection_ and _The Variation of Animals and Plants under Domestication_, will prepare the student for the long course of reading necessary for a full appreciation of what has been done in this department of science. From the numerous works which followed these I should select Bailey's _Survival of the Unlike_, London, 1896, and _Evolution of our Native Fruits_, New York, 1898, as especially useful for the reader of this book, to which may also be added _Plant Breeding_, New York, 1896, by the same author, as giving numerous facts and practical directions of value. Further, the "Hybrid Conference Report," _Journ. Roy. Hort. Soc._, 1900, abounds in facts and information. Rimpau, _Landw. Jahrb._, vol. xx., 1891, p. 239. The student who wishes to get towards the root of the matter will hardly be able to dispense with Strasburger's _Neue Untersuchungen über die Befruchtungsvorgang bei den Phanerogamen_, Jena, 1884. An interesting summary of recent work on _Xenia_ and "double fertilisation" will be found in _Bull. No. 22, U.S. Dept. of Agric._, 1900. See also _Nature_, Mar. 15, 1900, p. 470. If he wishes to explore the vast region of controversial literature that opens up from these points, and which is far beyond the purpose of this book, he may consult the literature collected in Kassowitz' _Allgemeine Biologie_, Wien, 1899, B. II., and the references in the works quoted; also, Strasburger, "The Periodic Reduction of Chromosomes in Living Organisms," _Ann. Bot._, viii., 1894, p. 281. For "Mendel's Law," see Correns in _Ber. d. deutsch. bot. Gesellsch._, vol. xviii., 1900, p. 158. _PART II._ DISEASE IN PLANTS. CHAPTER IX. PHYTOPATHOLOGY. DERIVATION AND MEANING. _History. References in the Bible--Greeks and Romans-- Shakespeare--Rouen law--Superstitions--Malpighi and Grew-- Hales--Unger--Berkeley--De Bary, etc. Physiology and Biology --Diagnosis--Etiology--Therapeutics. Study of causes._