THE RATE OF REPRODUCTION . 129 



up this rate long at a time. This rapidity of 

 reproduction is very valuable to them, since the 

 decaying food in which they thrive does not last 

 very long. This power enables them to make the 

 most of it. At this rate of increase, multiplying 

 by two every half hour, in one day it would 

 require twenty-eight figures to represent the 

 individual bacteria resulting from one parent; the 

 total would be two raised to the forty-eighth power. 

 Paramecium. Many of the one-celled animals live 

 on the same kind of decaying material as bacteria. 

 Some of them multiply at a rate nearly equal to 

 that in bacteria. Most, however, are not so rapid. 

 Paramecium, under favorable conditions, requires 

 from twelve to thirty hours to divide and grow to 

 maturity, but if its food held out and it could keep 

 up this rate, it would require only a few weeks for 

 the descendants of one Paramecium to make a 

 mass of protoplasm as big as the earth itself. 



Ferns. The fern produces spores only once a year, 

 but it produces millions at each season. If every 

 spore out of a million should succeed in producing 

 one mature fern plant, on the tenth year we would 

 have 1,000,000 to the tenth power of new fern 

 plants, to say nothing of all the old ones that lived 

 over from previous years. A single fern plant 

 could populate the earth with ferns alone in a few 

 years. 



The House Fly. Chancellor Jordan, of Leland 

 Stanford University, says concerning the reproduc- 

 tive power of this pest: "If all the eggs of a common 

 house fly should develop, and each of its progeny 

 should find the food and temperature it needed, 

 with no loss and no destruction, the people of a 

 city in which this might happen could not get away 

 soon enough to escape suffocation by a plague of 



