The time required to secure fixed types is variable, but in wheat and cotton, when careful experiments have been carried out and recorded, the indications are that four to six generations are ordinarily required to reach a fixed stage. This does not mean, of course, that all variation is prevented, but that the hybrids have been bred to the same type as nearly as is the case in any ordi nary race or variety.
Selection of vegetative parts.
No consideration of the methods of plant-breed ing would be complete without a mention of the improvements which can be produced by what may be termed the selection of vegetative parts. While, in general, all buds of a plant are practically the same, as is shown by the fact that buds taken from the Baldwin apple almost uniformly produce Bald win apples, yet there is considerable variation frequently in the product from different buds, and it is well known that we have a class of variations which we have corns to call bud-sports or bud-vari ations. In violets, for example, the propagation is normally by slips that are developed from different buds. These slips when grown into plants frequently show considerable difference, and Dr. B. T. Galloway and Mr. P. H. Dorsett, of the Department of Agricul ture, have demonstrated that, by the selection of slips from plants which are very productive, the yield in the number of flowers to the plant can be increased considerably. In the case of the orange, seedling trees are almost always very thorny, yet certain branches may show a tendency to be more nearly thornless, and by the selection of buds from such branches the thorny character of almost all the standard varieties has been reduced. By the sys tematic selection of vegetative parts, such as buds, slips, suckers, and the like, in many cases very important improvements could doubtless be secured, and the plant-breeder should have a thorough understanding of this method of improvement. In hybrids of mixed parentage frequently a bud on one side of a plant will sport, showing different tendencies, and many of our new varieties of roses, chrysanthemums and carnations have been pro duced by the selection of such bud-sports. Many standard varieties of carnations have produced bud variations that have proved valuable; the Lawson has given rise to the Red Lawson and White Lawson. The Enchantress has produced the Pink Enchantress and White Enchantress. The practice of exercising care in choice of chrysanthemum or carnation cuttings and of cions for fruit trees is therefore seen to rest on rational reasons.
The variations in the character of the seed from different bolls in the case of hybrid cottons, re ferred to on page 58, are bud-variations of this sort which, as pointed out there, may be of value to the breeder even in cotton which is propagated by seed. In the study of cotton, the writer has found similar bud-variations showing in the lint characters of hybrids. In quite a number of in stances, certain bolls have been found which pro duced much longer lint than other bolls on the same plant, and similar variations in strength and uniformity of length have been observed. Experi ments indicate that such variations, which are doubtless to be classed as bud-variations, are trans mitted in considerable degree, This being the case even in seed-propagated plants, it becomes desirable to observe and search for bud-variations.
Literature.
The principal general works are : Bailey, Plant Breeding, 4th edition, 1906, The Macmillan Co., New York ; Fruwirth, Die Zuchtung der Land wirtschaftlichen Kulturpflanzen, Berlin, 1904-06. The following are a few of the most important gen eral papers : Production et fixation des varietes dans les vegetaux, E. A. Carriere, Paris, 1865 ; Die Pflanzenmischlinge, W. 0. Focke, Berlin, 1881; A Selection from the Physiological and Horticul tural Papers of Thomas Andrew Knight, published in the Transactions of the Royal and Horticultural Societies, London, 1841 ; Hybrids and Their Utili zation in Plant-Breeding, W. T. Swingle and H. J. Webber, Yearbook, United States Department of Agriculture, 1897; Sur la production et la fixa tion des varietes dans les plantes d'ornement, Jean Baptiste Verlot, Paris, 1865; The Improvement of Plants by Selection, H. J. Webber, Yearbook, United States Department of Agriculture, 1898 ; Hybrid Conference Report, Journal Royal Horti cultural Society, Vol. NNW, April, 1900 ; Survival of the Unlike, Bailey ; Proceedings, International Conference on Plant-Breeding and Hybridization, New York Horticultural Soc. Memoirs, Vol. I, 1902; Proceedings of American Breeders' Association, Vols. I and II, Washington, D. C., 1905 and 1906; Breeding Animals and Plants, W. M. Hays, St. Anthony Park, Minnesota. Bailey's Plant-Breeding contains a very extended list of papers and books.