108 



INDEX 



Heiser, vii, 1, 74, 76 

 Helianthus, evolution under domesti- 

 cation, 75 



introgression in, 75 



origin of, 74 

 Helianthus Bolanderi, introgression in, 



76 

 Hemp, origin of, 67 

 Hevea, introgression in, 78 

 Hubbs and Hubbs, 90 

 H^'brid indices, 88 



details of construction, 89 

 Hybridization, artificial, history of, 21 



genetics of, 24 



intergeneric, 20 



interspecific, frequency of, 19 



new criteria for, 43 



prevalence summarized, 22 



restriction of habitat upon, 18 



usual results of, 100 



Zea and Tripsacutn, 20 



Ideographs, 86 



illustrated, 87 

 Imperata, 20 



Insect behavior, effect upon intro- 

 gression, 58 

 Introgression, between subspecies, 61 



character association caused by, 45 



defined, 1, 61 



diagram shomng importance of in 

 evolution under domestication, 

 69 



effect of insect behavior upon, 58 



effect of pastoral agriculture on, 79 



effect of rivers on, 63 



evolutionary importance of, 102 



in Cistus, 12 



in early post-glacial times, 65 



in fishes, 1, 21 



in Florida, 64 



in Helianthus, 75 



in Helianthus Bolanderi, 76 



in Hevea, 78 



in New Zealand, 80 



in the Ozarks, 65 



in Pinus, 62 



in Tradescantia, 16, 100 



Introgression, proof of, 45 



recognition of, in the field, 101 



relation to the gene theory, 80 



role in origin of domesticated plants, 

 66 



typical example, 2 



under natural conditions, 62 

 Introgressive hybridization, see Intro- 

 gression 

 Iris bremcaulis, 4 

 Iris fulva, 2, 94 



described, 2 



illustrated, 5 



variation tabulated, 3 

 7m fulva X /. hexagona var. giganti- 

 caerulea, artificial hybrids of, 4 



variation tabulated, 3, 94 

 Iris hexagona var. giganti-caerulea, 2, 

 94 



described, 2 



illustrated, 5 



variation tabulated, 3 

 Iris hybrids, character assocraition in, 



^ 45, 89, 94 

 Iris versicolor, 65, 87 

 Iris virginica, 65, 87 



Janaki-Ammal, 20 

 Jones, 37 



Lettuce, introgression in, 76 

 Lindegren and Lindegren, 13 

 Linkage, a factor in racial and specific 

 cohesion, 56 

 as a prehminary step in isolation, 59 

 cohesive effect of, 41 

 cohesive force of, in successive hy- 

 brid generations, 56, 57 

 effect on one multiple-factor char- 

 acter, 28 

 effects upon recombination, 36 

 example of its role in isolation, 59 

 hindrance to recombination, 39 



Mangelsdorf and Reeves, 20 

 Marie-Victorin, 80 

 Marsden- Jones and Turrill, 62 

 Mason, 63 

 Mather, 58 



