CHAPTER VI 



THE PHILOSOPHY OF THE CROSSING OF 

 PLANTS, CONSIDERED IN REFERENCE TO 

 THEIR IMPROVEMENT UNDER CULTIVA- 

 TION 



IT is now understood that the specific forms or groups 

 of plants have been determined largely by the survival 

 of the fittest in a long and severe struggle for existence. 

 The proof that this struggle everywhere exists becomes 

 evident on a moment's reflection. We know that all 

 organisms are eminently variable. In fact, no two plants 

 or animals in the world are exactly alike. We also know 

 that a very few of the whole number of seeds which are 

 produced in any area ever grow into plants. If all the 

 seeds produced by the elms upon Boston Common in 

 any" fruitful year were to grow into trees, the city would 

 become a forest as a result. If all the seeds of the rarest 

 orchids in our woods were to grow, in a few generations 

 of plants even our farms would be. overrun. If all the 

 rabbits which are born were to reach old age, and all 

 their offspring were to do the same, in less than ten years 

 every vestige of herbage would be swept from the country, 

 and our farms would become barren. 

 "The struggle for life. There is, then, a wonderful 



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