LIST OF ILLUSTRATIONS Xix 



FIGURE PAGE 



54. Schematic Curves of Head Height in Hyalodaphnia as Grown 



IN Media OF Three Different Food Values 332 



55. Climatic Effects upon Plumage in Pigeons 333 



56. Effects of Injections into Ovary of Scrophularia .... 335 



57. Diagram Illustrating Behavior of Chromosomes in Men- 



del's Cross of Tall and Dwarf Peas 347 



58. Dlagram Illustrating Behavior of First Hybrid Genera- 



tion When Inbred 34^ 



59. Dlagram Illustrating Dlhybrid Ratio 35 1 



60. Diagram Showing the Characteristic Pairing, Size Rela- 



tions, AND Shapes of the Chromosomes of Drosophila 

 melanogaster 3^^ 



61. Diagram of Mitosis in a Species Having Four Chromo- 



somes IN Its Cells 363 



62. The Reduction Division as Represented for a Species Whose 



Diploid Number Is Four 3^5 



63. Diagram of Chromatin Interchange between Homologous 



Members of a Pair of Chromosomes 3^7 



64. Diagram Showing Consequences of Independent Segrega- 



tion of Chromosomes in Drosophila melanogaster .... 368 



65. Diagram Showing Chromosome Relations in the Inheritance 



OF Sex in Drosophila melanohaster 37° 



66. DiAGR.\M Showing How the Original Scheme Must Be Modi- 



fied to Satisfy the Presence-and-Absence Hypothesis. . 373 



67. Diagram Showing How Presence-and-Absence Scheme Is 



Actually Used : 374 



68. Diagram Illustrating Blending Inheritance 375 



69. Diagram Illustrating Complementary Factors . . . . 377 



70. Diagram Illustrating Behavior of Inhibitory Factor . . 380 



71. Diagram Showing Some Possible Combinations in F^ When 



Fi OF Figure 70 Is Inbred 381 



72. Dlagram Showing THE Heterozygote Situation 381 



73. Diagram Illustrating THE Action OF A Supplementary Factor 382 



74. Dlagram Illustrating Nilsson-Ehle's Explanation of the 



15:1 Ratio in F2 of Hybrid between Red- and White- 

 grained Wheat 3^4 



75. Another Method of Visualizing Nilsson-Ehle's 15:1 Ratio . 385 



76. Diagram OF Nilsson-Ehle's 63 : 1 Ratio 386 



