180 



GENERAL BOTANY 



HYBRIDIZATION AND THE PRODUCTION OF NEW VARIETIES 



Hybridization is the crossing of plants of more distant rela- 

 tionship than the members of one species. Cross-fertilization 



between different 



varieties of culti- 

 vated corn, wheat, 

 barley, apples, and 

 carnations results 

 in what are known 

 as variety hybrids. 

 Crossings between 

 different species of 

 plants, for example 

 those between rasp- 

 berries and black- 

 berries, yield what 

 are termed species 

 hybrids. These are 

 apt to be sterile, 

 which accounts for 

 the fact that of cul- 

 tivated fruits and 

 vegetables compar- 

 atively few have 

 resulted from hy- 

 bridization. Unless 

 the cross-pollination 

 and fertilization take 



FIG. 93. Hybridizing wheat 



Note the operator with his tools : namely, a box contain- 

 ing strips of paper and pins for covering the wheat heads ; 

 tags for labeling; alcohol for sterilizing hands and in- 

 struments ; forceps and scalpel. The wrapped heads of 

 grain have already been pollinated and labeled. From 

 Babcock and Clausen's " Genetics in Relation to Agri- 

 culture." Photograph by William C. Matthews 



place between plants 

 which are too far 

 removed from each 

 other in relation- 

 ship, the offspring 

 will usually inherit increased vigor and also display a greater 

 variety of characters than is attainable by self-fertilization or 

 close-fertilization. This result is exactly what we should expect 



