CONTENTS xv 



PAGE 



Purpose and plan 342 



General method 343 



Method of hybridizing maize 344 



Method of hybridizing wheat 345 



Method of hybridizing alfalfa 348 



Some of the difficulties attending hybridization 350 



Conditions favorable for hybridization 351 



Species hybridization 351 



Svalof method of creating populations 352 



CHAPTER XX 

 UTILIZATION OF HYBRIDS IN PLANT BREEDING 



Introductory 353 



Purposes of hybridization 353 



Increased production in Fj maize hybrids 353 



Crossing inbred strains or biotypes 354 



Effect of inbreeding in strains of maize 355 



Method of comparing yields 356 



Crossing species, subspecies, varieties and strains 358 



Superior qualities of first generation hybrids 359 



Immediate effect of crossing on size of kernel 360 



Centralized seed corn production 361 



A method of producing hybrid corn seed 361 



Application in other annual crop plants 362 



Application in vegetatively propagated plants 364 



Rapid growing timber and ornamental trees 365 



CHAPTER XXI 

 MUTATIONS IN PLANT BREEDING 



Introductory 366 



Occurrence of mutations 366 



Mutations in crop plants 367 



The search for mutations 370 



Propagation of mutations 372 



CHAPTER XXII 

 GRAFT-HYBRIDS AND OTHER CHIMERAS 



Introductory 374 



Definition of graft-hybrid 374 



Winkler's tomato-nightshade graft-hybrids 374 



Baur's investigation of a natural chimera 378 



Other natural chimeras 381 



Two categories of variegation ... 381 



The physiological behavior of graft hybrids 382 



Modification of one graft-symbiont by the other 383 



