350 GENERAL SCIENCE 



farmers can still greatly improve most of the plants 

 which they grow by selecting seed from plants which show 

 an improvement caused by cross-fertilization. 



Sometimes cross-fertilization produces a plant that is 

 very different from the parent plants. When these far 

 different plants can be made to reproduce themselves, 

 a new variety comes into existence. New varieties of 

 corn, wheat, etc. have been produced in this way. 



239. Seedless Fruits. There are many so-called seed- 

 less fruits, such as navel oranges, lemons, bananas, and 

 pineapples. The method by which these are produced 

 is largely one of selection and by means of budding. 

 Seedless oranges, lemons, grapes, and bananas bloom 

 like other fruit trees. In the navel oranges the embryo 

 sac, which normally would develop into embryos and be 

 fertilized by the pollen, disintegrates before fertilization 

 takes place; hence they do not form seeds, but the fruit 

 develops as usual except that it is lacking in seeds. 

 Occasionally a few embryo sacs develop normally, and in 

 the event that these particular embryo sacs happen to 

 become fertilized by the pollen of a similar variety, there 

 will be seeds in fruit which is ordinarily seedless. For this 

 reason seeds are occasionally found in navel oranges. 



When a tree produces nearly all seedless oranges or 

 lemons, it is propagated by budding or grafting, that is, 

 a bud from the seedless orange tree is cut off and fixed 

 into the bark of a young orange tree in such a way that 

 it grows and forms a tree that produces seedless fruit 

 like the one from which the bud was taken. In case of 

 grafting, a twig is taken instead of a bud. In this way 

 many trees are soon grown from which buds for budding 

 can be selected from the trees that produce the most 

 seedless fruits. The young orange trees which are budded 



