226 Science of Plant Life 



from mutations that occurred among the currant tomatoes 

 or love apples grown for ornament in our great-grandmothers' 

 gardens. The original fruits resembled large red currants. 

 Today single tomato berries may weigh a pound. In color 

 they may be red, yellow, or pink, and in shape they may be 

 spherical, plum-shaped, pear-shaped, or flattened. They 

 exhibit at least three types of leaves and two types of stems. 

 The characteristics due to mutation are inherited, no matter 

 what the soil and climatic conditions may be. 



Mutations occur not only among plants grown from 

 seed, but also among plants, or plant parts, developed from 

 buds. These are called bud mutations, or bud sports. On 

 fruit trees, one branch will occasionally produce fruit that 

 is of different quality from the fruit produced on other 

 branches. If the quality of the fruit is superior, these 

 branches may be used in budding and grafting to preserve 

 the new variety. Bud sports are comparatively rare, but it is 

 estimated that at least several hundred horticultural varieties 

 have originated from them. In this country the improved 

 varieties of navel oranges have been secured entirely by this 

 method. The Boston fern and its forty or more varieties 

 originated in bud mutations from a wild tropical fern. In the 

 potato and some other plants that are usually propagated 

 vegetatively, bud variations are known to occur ; but they 

 are so jrare and so difficult to discover in plants of this kind 

 that they have not been of much practical value. 



Hybridization. The crossing of two species or varieties of 

 plants is known as hybridization. It is brought about by 

 transferring the pollen from one to the stigma of the other. 

 The plants grown from seed produced in this way are called 

 hybrids. Hybrids may resemble one of the parents, or they 



