CHAPTER XXX 

 THE STRUGGLE FOR EXISTENCE 



309. Meaning of the term. If we observe a dense forest or 

 a wheat field, we see that there are many kinds of plants that 

 are living under the shade of taller plants. Some of the 

 shaded plants seem to be thriving, and others may show by 

 their condition that they are not doing well. Likewise, along 

 a country roadside or in a vacant lot a great number of plants 

 often start to grow in a relatively small space. By observing 

 such a region at successive periods for some weeks it will usu- 

 ally be seen that fewer and fewer plants persist, and by the 

 time the seeds are ripe the number of plants that have matured 

 is small indeed compared with the number that began growth 

 at the beginning of the season. 



Similarly, in a pool of water there may be many hundreds 

 of small fish, tadpoles, and other types of animal life, but only 

 a few mature fish and frogs. 



310. Overproduction among plants. We shall get an idea of 

 how the crowded conditions upon the earth are caused if we 

 estimate the number of young that might possibly be produced 

 in a few years from any of our common plants or animals. An 

 ordinary morning-glory plant may bear 3000 seeds in one 

 season ; indeed, such a plant often bears considerably more 

 than that number. If each of these seeds should produce a 

 plant that bore 3000 seeds, at the end of the second year 

 there would be 3000 x 3000 seeds, or 9,000,000 seeds. If the 

 second year's crop of seeds should grow in the same way, at 

 the end of the third year there would be 27,000,000,000 seeds. 

 Similarly, if in the succeeding years all the seeds produced 

 should produce plants like the parent, this one plant with 



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