4 i2 NOTES OF A BOTANIST CHAP.XXIV 



This is a great advance on the views stated 

 in the earlier letter, in which he wrote : " The ants 

 cannot be said to be useful to the plants, any more 

 than fleas and lice are to animals ; and the plants 

 have to accommodate to their parasites as best they 

 may." The evidence, however, now shows that, in 

 all probability, they are always useful, in which case 

 their becoming hereditary is merely a question of 

 variability in the plant, and the continued preser- 

 vation of those whose variations were in the direc- 

 tion of utility to the ants. 



The whole of these very interesting phenomena, 

 so well described by Spruce, are thus seen to be in 

 complete accordance with those of the modification 

 of flowers by insect-agency, which are now admitted 

 to depend upon a mutual adaptation for the benefit 

 of both plant and insect. 



They lead, I think, to the establishment of the 

 general principle, that no special adaptation of one 

 organism to another can become fixed and hereditary 

 unless it is of direct utility to both.] 



