284 CONCLUDING EEMAEKS. Chap. IX. 



to use old wheels, springs, and pulleys, only slightly 

 altered, the whole machine, with all its parts, might be 

 said to be specially contriyed for its present purpose. 

 Thus throughout nature almost erery part of each living 

 being has probably served, in a slightly modified con- 

 dition, for diverse purposes, and has acted in the living 

 machinery of many ancient and distinct specific forms. 



In my examination of Orchids, hardly any fact has 

 struck me so much as the endless diversities of structure, 

 — the prodigality of resources, — ^for gaining the very 

 same end, namely, the fertilisation of one flower by 

 pollen from another plant. This fact is to a large ex- 

 tent intelligible on the principle of natural selection. 

 As all the parts of a flower are co-ordinated, if slight 

 variations in any one part were preserved from being 

 beneficial to the plant, then the other parts would 

 generally have to be modified in some corresponding 

 manner. But these latter parts might not vary at all, 

 or they might not vary in a fitting manner, and these 

 other variations, whatever their nature might be, which 

 tended to bring all the parts into more harmonious 

 action with one another, would be preserved by natural 

 selection. 



To give a simple illustration : in many Orchids the 

 ovarium (but sometimes the foot-stalk) becomes for a 

 period twisted, causing the labellum to assume the 

 position of a lower petal, so that insects can easily 

 visit the flower ; but from slow changes in the, form 

 or position of: the petals, or from new sorts of insects 

 visiting the flowers, it might be advantageous to the 

 plant that the labellum should resume its normal 

 position on the upper side of the flower, as is actually 

 the case with Malaxis paludosa, and some species of 

 Catasetum, &c. This change, it is obvious, might be 

 simply efi"ected by the continued selection of varieties 



