DARWIN'S DISCOVERIES 25 



which he discovered the mechanism and the wonderful 

 variety of movements of plants, and showed their value 

 to the plant, and consequent origin, by natural selection. 



He especially loved to discover evidence that plants 

 can do many things which had been thought to be only 

 within the powers of the other section of living things 

 the animals ; and finding during one summer holiday 

 that the beautiful little sun-dew moves its red-knobbed 

 tentacles so as to entrap minute insects, he discovered 

 the whole history of Insectivorous Plants, and showed 

 that there are many plants of various groups which catch 

 insects and digest them in a sort of stomach, as an animal 

 might do. Thus the water-holding pitchers of the pitcher- 

 plants of tropical forests were explained as being food- 

 catchers and digesters of great value to the nutrition of 

 the plant, and their gradual formation by variation and 

 natural selection rendered comprehensible. 



His greatest book next to the Origin containing an 

 immense quantity of original notes and observations and 

 valuable information from all kinds of breeders and fanciers 

 is the Variation of Animals and Plants under Domestica- 

 tion (1868). The facts recorded are discussed in the light 

 of the great theory, and honest, fair-minded consideration 

 is given to those which present difficulties as well as to 

 those which clearly favour it. In 1871 came the Descent 

 of Man, followed in 1872 by the Expression of the 

 Emotions in Men and Animals in which, again, it was 

 shown that the facts as to the likeness between man and 

 apes can be explained on the theory that natural selection 

 and survival of favourable variations have been at work, 

 and that the facts are hopelessly without meaning or ex- 

 planation on any other hypothesis. His last published 

 book was on The Formation of Vegetable Mould through 

 the Action of Worms, in which he not only showed what 

 an important part earthworms play in burying stones and 



