Table of Contents 



crossing on the species, 97 the limits of crossing, 97 



swamping effects of inter-crossing, 98 what deter- 

 mines the limits of crossing, 98 the limits of crossing 

 tend to preserve the identity of species, 99 the refusal 

 to cross, the result of natural selection, 100 for the 

 production of useful hybrids, do not have the parents 

 too diverse, 101 function of the cross, 101 rarity of 

 natural hybrids, 102 change of seed and crossing, 103 



results from change of stock, 105 crossing from 

 standpoint of plant improvement, 108 understanding 

 of terms, 108 history of plant hybrids, 110 what 

 plants can be hybridized, 111 vigor as a result of 

 crossing, 112 Darwin's experiments with morning- 

 glories, 114 Darwin's results with other plants, 115 

 increased vigor in other crosses, 115 three factors, 117 



the outright production of new varieties, 118 how 

 to overcome antipathy to crossing, 121 variability of 

 hybrids, 122 characteristics of crosses, 123 difficul- 

 ties in making successful crosses, 125 hybridization 



and asexual propagation, 125 in-breeding, 127 expe- 

 rience with egg-plants and squashes, 128 influence of 

 sex on hybrids, 138 uncertainties of pollination, 140 



graft hybrids, 142 the case of Cytisus Adami, 142 



Winkler's Solatium graft-hybrids, 146 are these 

 real graft-hybrids, 147. 



CHAPTER VII 

 HEREDITY .......... 



Heredity studied collectively, 149 the coefficient of 

 heredity, 152 notation, 153 conception of unit char- 

 acters, 154 knowledge of heredity has come through 

 experimental breeding, 154 rediscovery of Mendel's 

 work by de Vries and others, 155 Mendel's experi- 

 ments, 157 explanation of mendelian results, 166 

 explanation of diagram, 171 Mendel's results with the 

 offspring of hybrids in which several differentiating char- 



149-208 



