302 The Living Plant 



tending to check the other. Thus, many simple forms will not 

 form reproductive parts so long as the solutions in which they live 

 contain plenty of food, and the other conditions are favorable; 

 and it is only when they begin to feel the effects of insufficient 

 food or temperature that they will begin to form reproductive 

 bodies at all. Even in the higher plants the same principle holds, 

 and all farmers know that when soils are too heavily fertilized 

 many plants tend to "run to leaf," and flower very badly, while 

 there are plants of our greenhouses (e. g. Bougainvillaea) which 

 must actually be partially starved before they will form any 

 flowers. The same principle holds good with animals ; they must 

 not be too highly pampered and fed, else their reproductive powers 

 suffer. I believe that we have the operation of the same principle 

 upon a very large scale among mankind in the fall of the birth-rate 

 amongst the most highly civilized races, and the highest classes 

 of each race. In general the birth-rate is lowest where the hygienic 

 and other conditions are most favorable for the preservation and 

 comfort of the individual, and the birth-rate grows higher among 

 peoples and classes in which the conditions of life are markedly 

 harder. Harder conditions of life presage an earlier end to the 

 life of the individual, and Nature seems to have adopted their 

 presence as the stimulus or signal for setting the reproductive 

 apparatus more actively at work. 



