TABLE OF CONTENTS XV 



PAGE 



Chapter XXVII. The Physical Basis or Mendelism. E. B. Bab- 

 cock and R. E. Clausen 360 



Chapter XXVIII. The Factor Hypothesis as Applied to Plants. 



John M. and Merle C. Coulter 372 



Chapter XXIX. The Factor Hypothesis as Applied to Animals . 388 



Chapter XXX. Review of Mendelism and Introduction to the 



New Heredity 392 



Chapter XXXI. Sex Determination and Sex-linked Heredity . 396 



Sex Determination 39^ 



The Chromosomal Mechanism of Sex Determination .... 398 



Sex Differentiation 404 



Sex-linked Heredity 408 ^ 



Chapter XXXII. Linkage, Crossing-over, and the Architecture 



OF THE Germ Plasm 416 



Linkage 4i6 



Crossing-over 4^9 



Chromosome Maps Indicating the Arrangement of the Genes in the 



. Chromosomes 422 



Linkage in Other Organisms 427 



Chapter XXXIII. Biometry (The Statistical Study of Variation 



and Heredity) 43° 



The Statistical Study of Variation 43° 



The Statistical Study of Inheritance. E. G. Conklin 435 



Chapter XXXIV. Heredity in Pure Lines 441 



Chapter XXXV. The Origin of New Hereditary Characters . 445 



Chapter XXXVI. Are Acquired Characters (Modifications) 



Hereditary? 449 



Misunderstandmgs as to the Question at Issue. /. A. Thomson. . 449 

 The Inheritance or Non-Inheritance of Acquired Characters. E. G. 



Conklin 456 



The Other Side of the Question 462 



A Possible Mechanism for the Transmission of Acquired Characters. 



M. F. Gnyer 464 



Recent Experiments Believed to Favor the Lamarckian Theory . 471 



Chapter XXXVII. The Mutation Theory 475 



]<itw Species {Mutants) oi Oenothera. Htlgo De Vries 477 



Summary of De Vries's Mutation Theory. T. H. Morgan . . . 484 



