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accordingly) instead of having an upper and a lower 

 side (with a corresponding diiference in internal struct- 

 ure). The Potato furnishes another illustration; if the 

 young tubers be cut off as they are forming, the tuber- 

 forming material accumulates in the parts above 

 ground and produces tubers in the branches ; these are 

 green and bear leaves. Try both these experiments, if 

 possible. 



This influence of one part on another is called cor- 

 relation. Numerous other illustrations might be given; 

 it will suffice to mention the effect which the fertiliza- 

 tion of the ovary has on surrounding parts (see page 

 309). Experiments on this point may easily be made 

 by removing the anthers in the bud and preventing 

 pollination by paper bags. 



It is hoped that the facts set forth in this chapter 

 will lead to experiments when practicable, and to con- 

 stant observation of the experiments which are every- 

 where spontaneously occurring in garden and field. 



