96 THE METHOD OF DARWIN. 



seemed well worthy of investigation." 1 As 

 soon as he began to work on Drosera, and was 

 led to believe that the leaves absorbed nutri- 

 tious matter from the insects, he began to 

 reason by analogy from the well understood 

 digestive capacity of animals. One needs but 

 to imagine an attempt to do the work without 

 any knowledge of animal digestion to under- 

 stand at once its impossibility under such con- 

 ditions. By connecting his observations with 

 the well known animal processes he proceeded 

 on a course of rapid discovery that must other- 

 wise have remained entirely closed to him. At 

 almost every step he drew suggestions from 

 and checked his results by reference to animal 

 digestion. He made preliminary "crucial" 

 experiments by immersing some leaves of 

 Drosera in nitrogenous and others in non- 

 nitrogenous fluids of the same density to deter- 

 mine positively whether the former affected 

 the leaves differently from the latter. 2 The 

 discovery that Drosera detects "with almost 

 unerring certainty the presence of nitrogen " 

 in various fluids "led me to inquire," he said, 

 ''whether Drosera possessed the power of dis- 

 solving solid animal matter; the experiments 

 proving that the leaves are capable of true 



J Insectivorous Plants, p. 2. 2 Ibid., p. 76. 



