668 
Pigmentation, extent of, affected by modifying 
factors, 190 
in Drosophila and Leptinotarsa, 261 
modification of, in Coleus, 389 
Pine, Fi hybrids in, 365 
Pineapple, heterosis in, 364 
Piper, alfalfa, 296 
environment factors, 433 
Florida velvet bean, 367 
variety testing, 435 
Pisum sativum, 80 
linkage in, 125 
Plane, London, an F, hybrid, 365 
Plant breeding, beginning of, 287 
material, 299 
methods, 419 
classified, 291 
organization of, 299 
pioneers in, 288, 437 
progress, 291 
relation of science to, 437 
to genetics, 440 
breeders, organization of, 300, 301 
disease, 400 
groups, research on, 300 
improvement, earliest, 287 
introduction, 299 
populations, composition of, 317 
-to-row method, 337, 433 
Planting, methods of, 420 
Plants, crop, 288, 289, 302 
cross-fertilized, 317 
inheritance of sex, 212 
monecious and dicecious, 317 
reproduction in, 317 si 
self-fertilized, 317 
varieties in, 302 
Plough, crossing-over, temperature effect on, 120, 
121 
Plumcot, 297 
Plums, aphis-resistant, 297 
breeding, 297 
collections, 299 
hybridization, 311 
Pollen, grains of hybrids non-functional, 237 
preservation of, 350 
protection of, 343 
transportation, 300 
viability, 300 
Pollination, artificial, 343 
natural methods of, 317 
Polygamous plants, 318 
Polyphyletic origin of domestic animals, 460 
Pomace fly, see Drosophila ampelophila. 
Pomology, importance of bud selection, 391 
Poplar, Black Italian, an PF; hybrid, 365 
Poppy chimeras, 381 
Population, 37 
containing biotypes, 260 
nature of variations in, 317 
Populations, as affected by crossing, 321 
composition of plant, 317 
creating at Svaléf, 352 
normally self-fertilized, 320 
INDEX 
canadensis-trichocarpa, graft-hybrids, 
378 
F, hybrids in, 365 
generosa, a vigorous hybrid, 365 
Potato, at Svalof, 293 
' bud selection, 394 
certified seed, 397 
clonal selection, 298 
graftage of, 374 
heterosis in, 364 
ideal market tuber, 397 
Magnum Bonum, 290 
mutations in, 369 
running out or degeneration, 395 
sudden degeneration of, 397 
tuber-unit method, 395 
Potency of sex-factors, 217 
Poultry, see Fowls, ducks, etc. 
Powell, apple, 393 
Practical breeding, service of genetics to, 449 
importance of pure varieties, 341 
value of crossing corn, 361 
Predisposition to disease, inheritance of, 523 
Prepotency, fact of, 573 
factor potency interpretation, 575 
greater in male, 576 
hereditary complex interpretation, 575 
Mendelian interpretation, 574 
recognized, 501 
Presence and absence hypothesis, 153 
Primary non-disjunction, 199 
Primula, hybridization by Dutch, 287 
kewensis, chromosomes, 264 
sinensis rubra, 26, 134) 
Primrose, Evening, see Ginothera. 
linkage in Chinese, 125 
Principles of composition of populations, 324 
Pringle, hybridization, 292 
wheat rust, 411 
Pritchard, experimental error, 430 
sugar beet, 340, 369 
Probable error, 45 
experimental determination of, 430 
of a difference, 47 
significance of, 47 
Problems of animal breeding, 447 
of genetics, 4 
Progeny test, 291, 293 
Progress in plant breeding, 291 
Progression method of computing F2 genotypes, 
97 
Progressive mutations in Boston fern, 315 
Promiscuous crossing, results of, 343 
Propagation of mutations, 372 
Protection, of cultures, methods of, 420, 421 
of developing seed, 344 
of pollen in hybridization, 343 
of pollinated flowers, 344 
special devices, 344 
Proteins, specificity of, 266 
Protoplasm, problem of nature of, 268 
Protoplasmic constituents, molecular structure, 
266 
Prunus, research on, 300 
Populus, 
Digitized by Microsoft® 
