Hitherto plant-breeders have made great ress in methods of procedure, and have many new varieties of fruit, grain, and flowers, but have learned little of the principles control ling aml limiting the production of new varieties. Serious efforts are being made by many investiga tors to establish a scientific basis for plant-breed ing experiments. ln August. 1899, an interna tional conference of hybridists was held in Lon don under the auspices of the Royal 'Horticultural Society of England. This meeting. which was at tended by ninny of the leading plant-breeders and scientists interested in the subject, served to arouse activity on the part of many and the liter ature of the subject has since considerably in creased. De Vries, Correns, Tsehermak, Bateson, Hays, Spillman, and others have written exten sively of their work in this generation of new varieties, and have sought to deduce laws govern ing the phenomena of variation. This awakened energy led to the almost simultaneous discov ery by Correns, De Vries, and Bateson of a paper entitled "Versuche fiber Pflanzenhybriden," published in 1865 by “regor Mendel. who showed that nearly constant numerical ratios could lie obtained among the types produced by hybridiza tion. As yet the reason why sonic (diameters are transmitted and others are not is not clearly un derstood, lint so far as Mendel's is concerned the :ipproximate proportions in which certain prominent eharaiders will appear in the can be foretold. In the cross-breeding of Mendel two characters were selected, called re spectively the dominant and the recessive. If these characters have been well fixed in the par ent plant, they will appear in the hybrid offspring in a regular mathematical proportion, which may be hriidly by the formula 1D: 21)R: IR. In these 1) and IT continue to exhibit pure
dominant and recessive characters and the 21)R furnishes the true crosses which continue to vary in the same proportion as in the formula. This applies to crosses of plants whose ancestors are equally pure and fertile. Most of the exceptions to the so-ealled Mendellian law can prohablv he explained by either of these possible sourees of error. For a full discussion of Mendel's law-. con sult Bateson. Mendel's Principles of Heredity (London, 1902).
Tn 1902 a second International Conference on Plant Breeding was held in New York City, der the auspices of the New York Ilortieultural Society. Papers were read by many of the fore most plant-breeders of the world, and the results of numerous experiments were shown by the origi nators of many new varieties of cereals, fruits, and flowers. The papers are printed in the Tra ns act ions of the society and a brief abstract of them is in Experiment Motion Record, X i V., I). For further information, see New Jersey Ex periment Station Peport for 1901, in which the plant-breeding work of the American Experiment Stations is summarized ; United States Depart ment of Agriculture Year Books, 1897, 1898,1899; Experiment Station Record, vols. xi., xis., Correns, notanische Zeit ling, 1900; De Vries, Die .11utations-Thcorie (Leipzig, 1901) ; Weldon, Biometrika, vol. i., part 2 (1902) ; Tsehermak, Zt itschrift fi&r/andirirtschaftliehes Versuelistecscn in Vest ureic!' (1900-01) ; Vernon, Variation in Animals and Plants (New York, 1903). Sec BREEDS AND BREEDING, paragraph Piont-Brccditly.