THE LIFE AND WORK OF DARWIN 219 



investigated, and the causes producing them reduced 

 to simple laws. 



"Insectivorous Plants" was a typical piece of 

 Darwinian work. " In i860," he says, " I was 

 idling and resting near Hartfield, where two species 

 of Drosera abound, and I noticed that numerous 

 insects had been entrapped by the leaves. I carried 

 home some plants, and on giving them some 

 insects, saw the movements of the tentacles, and this 

 made me think it possible that the insects were 

 caught for some special purpose. Fortunately, a 

 crucial test occurred to me, that of placing a large 

 number of leaves in various nitrogenous and non- 

 nitrogenous fluids of equal density ; and as soon as 

 I found that the former alone excited energetic 

 movements, it was obvious that here was a fine new 

 field for investigation." 



These researches showed that the plants secreted 

 a digestive fluid like that of animals, and that insects 

 were actually used as food. 



The " Power of Movement in Plants," a tough 

 piece of work, was published in 1880. "In accord- 

 ance with the principles of Evolution it was im- 

 possible to account for climbing plants having been 

 developed in so many widely different groups, unless 

 all kinds of plants possess some slight power of 

 movement of an analogous kind." 



We come now to the last of his books, a singularly 

 interesting and most characteristic piece of work. 

 On the 1st of November 1837 — i.e., about a year 

 after his return from the voyage of the Beagle — 

 Darwin read a paper before the Geological Society 



