12 HORTICULTURE FOR SCHOOLS 



mutations, and bud-selection is useful not alone for the pur- 

 pose of perpetuating more desirable forms, but also of avoid- 

 ing the use of those that are less desirable. It is supposed to 

 be specially efficacious in promoting productivity. 



21. Ways in which plants vary. Sometimes plants may 

 be made to vary with regard to chemical contents of root, 

 stem, leaf, or fruit. An excellent example is afforded by the 

 sugar-beet, which, in the course of twenty-five years, was so 

 changed by breeding and selection that the average sugar- 

 content was raised from 6 to 15 per cent, and in exceptional 

 cases, as high as 22 or 23 per cent. Another example of such 

 variation is the changing of the proportion of protein to 

 starch in Indian corn. In the corn used for the manufac- 

 ture of corn-starch, the starch-content of the grain has been 

 increased materially, and the protein-content decreased. Still 

 another example is the increase in the proportion of sugar in 

 plums; the prune is a plum in all respects except that it 

 has sufficient sugar to enable it to be dried without remov- 

 ing the pit. This addition of sugar has been secured by 

 means of selection with regard to sugar-content through 

 a long period of years. Plants may be improved in respect 

 to the size of their fruits. The wild crab is very small 

 in comparison with the cultivated apple. Varieties of 

 blackberries produce fruits differing greatly in size. The 

 same is true of the tomato and many other cultivated 

 plants. 



Again, plants may be made to change with respect to their 

 resistance to frost and the time of ripening of the fruits. 

 Bailey states that apples not suited to our northern climate 

 have been changed by crossing with Siberian crab-apples 

 so that the area adapted to apple-growing has been extended 

 northward. The peach is particularly susceptible to frost- 

 injury; yet it is grown successfully today on both the Ameri- 

 can and Canadian side of the Great Lakes, as well as in Nova 

 Scotia. This is largely the result of the securing of varieties 



