THE STRUGGLE FOR EXISTENCE 375 



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. 



387. Overproduction among plants. We shall get an idea 

 of what causes the crowded conditions upon the earth if we 

 estimate the numbers that might be produced if all the young 

 might grow to maturity. 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, the one plant with which we began would in five years 

 produce 243,000,000,000,000,000 seeds. If there is an aver- 

 age of 20 feet of vines to each plant, the total length of the 

 vines of the sixth-year crop would reach over 36,000,000,000 

 times around the earth. Since light travels 186,000 miles 

 per second, how long would it take for it to travel the length 

 of the sixth-year crop of morning-glory plants ? 



Another illustration may show in a better way the possi- 

 bilities of plant production. A common kind of garden sweet 

 corn may have 4 good ears on a stalk, 12 rows of grains on 

 each ear, and 20 grains in each row. Therefore one ear may 

 have 240 grams upon it, and one plant may have 960 grains. 

 If each grain produces a new plant the next year, and this 

 process continues for five years, the fifth-year crop will con- 

 sist of 3,397,346,240,000 ears. That would be over 30,000 

 ears for each person in the United States, or two ears per day 

 for each man, woman, and child for over fifty years. 



