294 CONCLUDING REMARKS [Chap. XV. 



capable of true digestion, the solvent just referred to, which 

 must be occasionally present in the glands, would be apt to 

 exude from the glands together with the viscid secretion, in- 

 asmuch as endosmose is accompanied by exosmose. If such 

 exudation did ever occur, the solvent would act on the ani- 

 mal matter contained within the captured insects, and this 

 would be an act of true digestion. As it cannot be doubted 

 that this process would be of high service to plants growing 

 in very poor soil, it would tend to be perfected through natu- 

 ral selection. Therefore, any ordinary plant having viscid 

 glands, which occasionally caught insects, might thus be 

 converted under favourable circumstances into a species 

 capable of true digestion. It ceases, therefore, to be any 

 great mystery how several genera of plants, in no way closely 

 related together, have independently acquired this same 

 power. 



As there exist several plants the glands of which cannot, 

 as far as is known, digest animal matter, yet can absorb salts 

 of ammonia and animal fluids, it is probable that this latter 

 power forms the first stage towards that of digestion. It 

 might, however, happen, under certain conditions, that a 

 plant, after having acquired the power of digestion, should 

 degenerate into one capable only of absorbing animal matter 

 in solution, or in a state of decay, or the final products of 

 decay, namely the salts of ammonia. It would appear that 

 this has actually occurred to a partial extent with the leaves 

 of Aldrovanda; the outer parts of which possess absorbent 

 organs, but no glands fitted for the secretion of any diges- 

 tive fluid, these being confined to the inner parts. 



Little light can be thrown on the gradual acquirement 

 of the third remarkable character possessed by the more 

 highly developed genera of the Droseracece, namely the power 

 of movement when excited. It should, however, be borne in 

 mind that leaves and their homologues as well as flower- 

 peduncles, have gained this power, in innumerable instances, 

 independently of inheritance from any common parent form; 

 for instance, in tendril-bearers and leaf-climbers (. e. plants 

 with their leaves, petioles and flower-peduncles, Ac, modi- 

 fied for prehension) belonging to a large number of the most 

 widely distinct orders, in the leaves of the many plants 



