LIST OF ILLUSTRATIONS xv 



FIG. P^GE 



55. Cross between a mutant type of one species of snapdragon 



and a normal type of another species 97 



56. Different recombination types resulting from cross of two 

 species of snapdragon (figure 55) 98 



57. Varieties of two species of Helix, and hybrid between them . 99 



58. Drosophila melanogaster and D. simulans 100 



59. Homologous genes of Drosophila melanogaster and D. simu- 

 lans 101 



60. Chart of chromosomes of Drosophila virilis 102 



61. Chart of chromosomes of Drosophila obscura 103 



62. Chromosomes of Metapodius with three m-chromosomes and 

 their reduction 106 



63. First two divisions of egg of Ascaris 108 



64. Polar, metaphase group of chromosomes of diploid and 

 tetraploid Artemia 109 



65. Diploid and tetraploid chromosome group of Oenothera . . 110 



66. Maturation of pollen mother cells of Oenothera .... Ill 



67. Grafting of tomato and nightshade, and a resulting chimaera 113 



68. Dij^loid and tetraploid nightshade 114 



69. Seedlings, flowers, and cells of diploid and tetraploid night- 

 shade 115 



70. Haploid and diploid cells of normal nightshade; diploid and 

 tetraploid cells of tetraploid 116 



71. Same of tomato 117 



72. Normal and tetraploid Datura 118 



73. Haploid, diploid, triploid, and tetraploid Datura .... 119 



74. Diploid and tetraploid chromosome groups (second matura- 

 tion division) of Datura 120 



75. Methods of conjugation of chromosomes of diploid, triploid, 



and tetraploid Datura 121 



76. Conjugation of chromosomes of tetraploid Datura . . . 122 



77. Chromosome groups of Euehlaena, annual and perennial, of 

 Indian corn, and of hvbrid 123 



78. Diagram of gametophyte and sporophyte generation of dioe- 

 cious moss 125 



79. Diagram of formation of 2n gametophyte from regeneration 

 of 2n sporophyte, and 4n gametophyte by regeneration from 



4n sporophyte 127 



80. Triploid chromosome-group of hyacinth 132 



81. Maturation division of diploid and triploid Datura . . . 133 



