The Office of Flowers 



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173. Cross-Fertilization is Important in many plants. 

 There are many plants that are normally self-fertilized 

 and whose progeny do not seem to lack vigor. However, 

 most plants give better seed from cross-fertilization, 

 that is, having the pollen to come from different plants. 

 Seeds originating from normal cross-fertilization are 

 usually more vigorous, healthy and productive than 

 seeds resulting from self-fertilization. The Illinois 

 experiment station found a difference of about ten 

 bushels per acre in 

 the yield of corn 

 between seed pro- 

 duced by cross- 

 fertilization (Fig. 

 58) and that by 

 self-fertilization. 



C ont inuous 

 self- fertilization 

 leads to complete 

 sterility in plants 

 that are normally 

 cross-fertilized, as 

 corn, etc. Fig. 59. 

 Darwin found 

 that after* eleven 

 generations of 

 self- fertilization 

 the scarlet runner 

 failed to set seed, 

 while the plants 

 produced by as 

 many generations by cross-fertilization were much 

 more healthy and fruitful than the original stock. 



Fig. 59. Effect of inbreeding. A, Cross-bred; B, 

 inbred five years. From Bulletin, Illinois Ex- 

 periment Station. 



