360 TEXTBOOK OP BOTANY 



for which they were grown. Long ago no one can say just 

 when men learned that the seeds of large plants are more 

 likely to produce large plants than the seeds of small ones 

 are, and that the seeds of a plant with large fruits are, on the 

 whole, most likely to produce plants with large fruits. So, 

 here and there, growers began to pick out and to sow the 

 seeds of those particular plants which seemed to them most 

 valuable. This kind of selection was the beginning of plant 

 breeding, which therefore goes back a long way. But it is 

 only in rather recent times that breeding has been carried on 

 according to definite plans and on a large scale. 



373. What Plant Breeders Try to Do. One of the most 

 important things to be considered in the breeding of a variety 

 of plants is its yield of fruits, seeds, flowers, or other useful 

 parts. Sometimes breeders aim at a high yield for each in- 

 dividual plant each apple tree, or rose bush, for example. 

 But often it is more important to consider the yield of all the 

 plants that can be raised in an acre or in some other limited 

 area ; for a greater yield may often be obtained from a large 

 number of small plants, each one yielding comparatively 

 little, than from the smaller number of large plants that 

 might be raised on the same piece of land. 



Closely related to the question of yield is that of the length 

 of the season during which the plant produces flowers or 

 fruits. As a rule, a particular sort of plant has a short 

 bearing season, ranging from a few days to a few weeks. 

 Sometimes this period may be lengthened by breeding ; thus, 

 rose varieties have been developed that bloom at intervals 

 throughout the whole summer. But more commonly the 

 same end is reached by breeding different varieties which 

 bear at different times ; and so we have early and late cher- 

 ries, early and late apples, and early and late ' potatoes. 

 Early varieties are likely to be especially valuable ; the 

 highest prices are paid for the first strawberries or the first 

 peaches that appear in the market ; and so it is well worth 



