1366 



PLANT -BREEDING 



PLATANUS 



types can be selected. It is thus important that the 

 hybrids of the first generation should be inbred with 

 their own pollen or with pollen of the hybrids of the 

 same combination, and numerous individuals of the sec- 

 ond generation obtained in which plants showing the 

 desired combination of characters are more likely to 

 be found. 



One of the most prominent characters of crosses is 

 their extreme vigor, which is particularly marked in 

 racial and specific hybrids where the parents are widely 

 distinct in characters (Fig. 1845). In crosses of closely 

 related sorts, which are reproduced by buds, cuttings, 

 slips, etc., and which do not ordinarily remain true to 

 type when propagated by seed, the increase in vigor is 

 not commonly so marked. 



Sterility, which is a common character of hybrids of 

 very distinct species and races, may prove a detriment 

 in certain cases; but it is seldom that all of the hybrids 

 of any combination are completely sterile, and in most 

 instances of this sort complete fertility can probably be 

 secured by selection. 



The improvements which can be secured by means of 

 crossing are almost innumerable, and many of them, so 

 far as we are informed, can be secured in no other way. 

 Such is the production of fragrant varieties from odor- 

 less types as has been accomplished in the case of pan- 

 sies, and the blending and changing of colors of flowers 

 and fruits. Increased hardiness and adaptability to 

 growth in warmer climates might possibly be secured 

 by simple selection through a long series of years ; but 

 they can doubtless be most quickly secured by crossing 

 tender and hardy sorts or species, when plants can be 

 obtained which possess these opposite qualities. 



Fixation of Crosses. In plants which are propagated 

 by vegetative parts no fixation is necessary, but in those 

 which are propagated by seed, all crosses that are 

 found to possess desirable qualities must be fixed by 

 selection into stable races reproducing these qualities 

 true. Usually, a large majority of the progeny of a cross 

 will revert toward one of the parents, and may not 

 show the characters desired. In order to render the de- 

 sired qualities hereditary, the cross must be inbred 

 with its own pollen or the pollen of another cross of 

 the same parentage which exhibits the same characters, 

 and a large number of plants grown from the seed thus 

 produced. These plants must then be carefully exam- 

 ined and individuals selected for further work which 

 have reproduced the desired characters in the highest 

 degree. These individuals must be again inbred and the 

 process continued for several generations until all of the 

 plants are reproduced true to the desired type. This, 

 in most cases, requires from five to six generations of 

 careful selection. The time used in selecting to fix the 

 type is by no means lost, as meanwhile careful attention 

 can be given to increasing the fruitfulness so that this 

 factor also mav be greatly improved. 



this way. In orchard fruits, carnations, violets, pota- 

 toes, etc., careful attention should thus be given to the 

 buds or cuttings used in propagation. By a careful 

 selection of violet cuttings from those plants which 

 were found to produce the greatest number of good 

 flowers, P. H. Dorsett has greatly increased the average 



a & c ._.. 



1844. Cotton flowers, illustrating the process of emasculation- 



a, mature bud showing the stage which should be 

 selected for emasculation ; 6, a similar bud with the 

 corolla cut off ready to emasculate ; c, a similar bud 

 with the stamens removed, emasculated. 



THE SELECTION OP VEGETATIVE PARTS. Within re- 

 cent years some attention has been given to the im- 

 provement of plants by the selection of buds, cuttings, 

 etc., and the results obtained by certain practical in- 

 vestigators indicate that much may be accomplished in 



F H M 



1845. Increase in size of cotton bolls caused by hybridization. 



F, Sea island cotton used as the female parent ; If, 

 hybrid ; M, Klondike, a variety of upland cotton used 

 as the male parent. 



yield of his plants and believes that an increased yield 

 of nearly 100 per cent is perfectly possible by careful 

 attention to this factor alone. Here, again, it is not in- 

 creased yield merely which can be improved, but various 

 other qualities as well. 



The literature of plant-breeding is mainly scattered 

 through periodicals and is difficult of access. The prin- 

 cipal work treating the subject in a general way is 

 Professor Bailey's "Plant-Breeding" (The Macmillan 

 Company, New York, 1895). The following are a few of 

 the most important general papers: "The Production et 

 Fixation des varie'te's dans les ve"ge"taux," by E. A. Car- 

 riere, Paris, 1865; "Die Pflanzenmischlinge," by W. O. 

 Focke, Berlin, 1881; "A Selection from the Physiologi- 

 cal and Horticultural Papers of Thomas Andrew Knight, 

 published in the Transactions of the Royal and Horti- 

 cultural Societies," London, 1841; "Hybrids and their 

 Utilization in Plant-Breeding," by W. T. Swingle and 

 H. J. Webber; Year-book, U. S. Department of Agri- 

 culture, 1897; "Sur la Production et la Fixation des 

 Varietes dans les Plantes d'Ornement," by Jean Bap- 

 tiste Verlot, Paris, 1865; "The Improvement of Plants 

 by Selection," Yearbook, U. S. Department of Agricul- 

 ture, 1898; "Hybrid Conference Report," Journal Roy. 

 Hort. Society, vol. xxiv, April, 1900 ; " Survival of the 

 Unlike," by Bailey. HERBERT J. WEBBER. 



PLANT CELLAKS will be treated under Winter Pro- 

 tection. 



PLATANUS (its ancient Greek name). Platandcece. 

 PLANE-TREE. BUTTONWOOD. Ornamental deciduous 

 trees with alternate, petioled, rather large, palmately 

 lobed Ivs. and small greenish flowers in globular, soli- 

 tary or racemose, slender-stalked and drooping heads, 

 followed by similar heads of fruits remaining on the 

 branches during the winter. The smooth, light-colored 

 often almost creamy white bark of the branches and 

 limbs, usually mottled by darker blotches of the older 

 bark, which peels off in large thin plates, gives the 

 tree a very characteristic appearance in winter, while in 

 summer the Plane-tree, with its large head of dense 

 bright green foliage and with its massive trunk, is a 

 beautiful and majestic shade tree. The native Platanus 

 occidentalis is hardy north and P. orientalis hardy as 

 far north as Mass., while the southwestern and Mexican 

 species cannot be cult, in the North. From time imme- 

 morial the Oriental Plane, which was well known to the 

 ancient Greek writers, has been famous for the large 



