THE MOVEMENTS AND HABITS OF PLANTS. 21 



out nature almost eyery part of each living being has 

 probably served, in a slightly modified condition, 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 fertilization of one flower by pollen 

 from another plant. This fact is to a large extent in- 

 telligible on the principle of natural selection. As all 

 the parts of a flov?er 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. 



AN ILLUSTEAXION. 



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 in- 

 sects 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, etc. This change, it is obvious, might be 

 simply effected by the continued selection of varieties 

 which had their ovaria less and less twisted ; but, if the 



