Page:The New International Encyclopædia 1st ed. v. 16.djvu/122

* PLANT-BREEDING. 94 PLANTIGRADE ANIMALS. employed in all selection experiiiieiits, and fixed chuiaeurs .should be si'lectcd as far as possible. A knowledge of the following correlations will aid tlic plant-breeder: Small foliage is usually asso- ciated with small fruit: dwarf seedlings produce poor plants; palecoloreil foliage is usually an ac- companiment of light-colored fruit, llowcrs, etc.; large individuals are incompatible with numerous specimens, great productiveness with extreme earliness, and very great size with intense colora- tion. By paying" attention to these principles a skillful plant-breeder can inlhn'iice almost at will the external characters of form and color and the internal qualities of llavor, ]icrfume, and chemical composition. It is (piite as possible, however, for varieties to degenerate unch'r selection as to im- j)rove, and this fact shows the importance of mak- ing the i)roper .selection and constantly keeping it in mind in .subsequent selections. Hitherto ijlant-breeders have made great prog- ress in nietlioils of procedure, and have produced many new varieties of fruit, grain, and llowers, but liave learned l.iltle of the jiriiiciples control- ling and limiting th<' production of new varieties. Serious efforts are being made liy many investiga- tors to establish a scientitic liasis for jdant-breed- ing ex]H'riments. In August, 18!)!), an interna- tional conference of hybridists was held in Lon- don under the auspices of the Koyal Ilcuticultural Society of Kngland. This meeting, whidi was at- tended by many 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. Be Vrics, Correns, Tschermak, Bate.son, Hays, Spillman, and others have written exten- sively of their work in the generation of new varieties, and have sought to deduce laws govern- ing the ])lienomena of variation. This awakened energy led to the almost simultaneous discov- ery by Correns, De Vries, and Uateson of a paper entitled "X'crsuche fiber Pllanzenhybriden," l)ul)lished in lS(i.5 by (Jregor Jlendel, who showed that nearly constant numerical ratios could be obtained among the ty])es produced by hybri<liza- tion. As yet the reason why some characters are transmitted and others are not is not dearly un- derstood, but so far as Jlendel's worlc is concerned the ajiproximate proportions in which certain prominent characters will appear in the ofTspring can be foretold. In the cross-breeding ex])eriments of Mendel two characters were selected, called re- spectively the dominant and the recessive. If these cliaraeters have been well fixed in the par- ent plant, they will appear in the hylirid olTs|)ving in a regular mathematical proportion, which may be rejiresentecL brielly by the formula ID: 2DR : IR. In these V> ;ind H continue to exhiliit ])ure dominant and recessive characters and the 2DR 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. Host of the exceptions to the so-called Mendellian law can ])rol)ably he explained by either of these possible sources of error. For a full discussion of Mendel's hiw. con- sult Bateson, Mctulel's Principles of Heredity (London, 1002). In 1002 a second International Conference on Plant Breeding was held in New York City, un- der the auspices of the New York Horticultural 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 llowers. The papers are printed in the 'I'nins- actions of the society and a brief abstract of them is given in Ejojierinicnt NIaliun Hccord, xiv., p. 208. For fuither information, see New Jersey Ex- periment Htutiun li'eport fur li)t, in which the plant-breeding work of the American Experiment Stations is summarized; United States Depart- ment of Agriculture Year Books, 1897, 1898,18!)9; Experiment Station Uecord, vols, vi., xi., xiv., Correns, liotanische Zeitung, lUOO; De Vries, Die M utations-Theorie (Leipzig, 1901) ; Weldou, Biometrika, vol. i., part 2 (1!)02): Tschermak, Zeilschrift fiiir la ndir i rl selia f 1 1 iehes Versiiclistccsen in Oesterreieh (1900-01); Vernon, Variation in Animals and I'lants (New York, 191)3). See Brekus and BREEniNG, paragraph I'lant-Brcediny. PLANT-BUG. Any one of several families of true bugs, which feed upon plants by extract- ing the sap through the beaks. The Coreid;e are a very large and important family, containing , more than 1.500 species. The squash-bug (see Squash Insects) is a representative of this group, as also is the box-elder plant-bug (Lepto- coris trivittatus), a species which frequently damages the box-elder trees that, because of their rapid growth, are commonly planted on Western tree claims. The Pyrrhocoridie are a much smaller group, but include several well-known species. The red-bug or cotton-stainer, which does considerable damage to cotton in Flor- ida, as well as to the orange groves, is a promi- nent example. The family Lyga!id<-e is another of the largest families of plant-bugs, comprising more than 1300 species distributed in 13 sub- families and 208 genera. About 175 species are known in the United States. The most prominent member of this family is the chinch-bug ( of the Colorado potato-beetle, and is sometimes called the 'potato-bug enemy.' See Cotton In- sects. Consult: Comstock, jdanttal for the Study of Insects (Ithaca, 1895) ; Howard, The Insect Book (New Y'ork, 1902.) PLANT-CUTTER. One of the tanager-like liirds, related to th(^ cotingas (q.v.), and to the American lly-catchers. They constitute a small family (PhytotomidaO, and show some remarka- ble anatomical peculiarities. The bill is sliort, strong, conical, with lateral margins finely ser- rated. The intestine is sliort, an unusual condi- tion in vegetable-eating birds. They live in pairs or in small flocks and commit depredations in orchards and gardens by cutting off plants, buds, and fruits. They also catch insects. There are three species, all natives of temperate South America, the best-known of which is the 'rara' {Phytotoma rara) of Chile, of the size of the com- mon thrush, and of reddish brown and white plumage. It has a short low flight, and a dis- agreeable rough note. See Plate of COTINGAS, ETC. PLAN'TIGRADE ANIMALS (from Lat. pliinta. sole of the foot -|- yradi. to walk). Ani- mals that have the font so formed that the whole sole touches the groiuid in walking. Man and the bear are examples. The term is used in opposi- tion to 'digitigrade.' or walkini: on the tips of the toes, like the horse and dna. Between plantigrade and digitigrade animals all sorts of gradations in- tervene.