276 THE LIFE OF THE PLANT 



sweet sap and therefore serve to attract insects, and 

 also very smooth surfaces over which the insects cannot 

 help sHding down into the trap, and lastly, hard hairs 

 with tips turned inwards to prevent the victim from 

 coming out of its trap. But what is this liquid secreted 

 by the plant, what is this process by which the solid 

 food is dissolved, and has it anything in common with 

 what we generally call the digestion of food in an animal 

 organism ? As we have already seen,^ careful investi- 

 gations have proved that there is a remarkable similarity 

 between these two processes. 



As in the gastric juice of animals, in which the dis- 

 solution of albuminoids takes place under the influence of 

 a special ferment, pepsin, so also in the liquids secreted 

 by all insectivorous plants the presence of a ferment 

 has been discovered. Just as there pepsin acts only in 

 presence of a small quantity of free acid, so also here, 

 at the moment when the plant is irritated, an acid 

 reaction of the secretion can be easily demonstrated.^ 



Thus the process of nutrition cannot afford us any 

 sure criteria for differentiating plants from animals : 

 fungi, parasites, and especially insectivorous plants, 

 present a complete analogy with the nutrition of 

 animals. In fact, if, taking into consideration all that 

 has been said about these plants, we had described an 

 imaginary organism, which by means of antennae 

 caught insects and conveyed them into a cavity of 

 its body covered with glands ; if, moreover, we had 

 said that these glands secreted a juice that dissolved 



1 See chapter iii. 



' Recently doubts have arisen as to the utiUty for the plant of this 

 absorption of organic matter. While paying a visit to Darwin I had an 

 opportunity of seeing some unpublished experiments of the great 

 scientist, which prove the significance of the process above described from 

 the point of view of nutrition. Several sundew plants were grown by him 

 under a glass bell, so as to save them from insects. Half of them received 

 meat, half did not. At the time I saw them (in July) the plants which 

 received meat were iax bigger and more healthy in appearance than the 

 others (Note to the first edition.) 



