Chaf IX. CONCLUDING KEMAEKS. 275 



compelling insects to visit the flowers in front. Few 

 persons now doubt the correctness of C. K. Sprengel's 

 view,* that the bright and conspicuous colours of 

 flowers serve to attract insects from a distance. Never- 

 theless some Orchids have singularly inconspicuous 

 and greenish flowers, perhaps in order to escape some 

 danger ; but many of these are strongly scented, which 

 would equally well serve to attract insects. 



The labellum is by far the most important of the 

 external envelopes of the flower. It not only secretes 

 nectar, but is often modelled into variously shaped 

 receptacles for holding this fluid, or is itself rendered 

 attractive so as to be gnawed by insects. Unless the 

 flowers were by some means rendered attractive, most 

 of the species would be cursed with perpetual sterility. 

 The labellum always staads in front of the rostellum, 

 and its outer portion often serves as a landing-place 

 for the necessary visitors. In Epipactis palusiris this 

 part is flexible and elastic, and apparently compels 

 insects in retreating to brush against the rostellum. 

 In Cypripedium the distal portion is folded over like 

 the end of a slipper, and compels insects to crawl out 

 of the flower by one of two special passages. In Ptero- 

 stylis and a few other Orchids the labellum is irritable, 

 so that when touched it shuts the flower, leaving only 

 a single passage by which an insect can escape. In 

 Spiranthes, when the flower is fully mature, the column 

 moves from the labellum, space being thus left for 



* This nutlioi's cniiniis work, own observalioiis, tliat his work 



with its quaint title of ' Das Eiit- contains an immense body of 



J.cckte Geheimniss der Natur,' truth. Many years ago Kobert 



until lately was often spoken Brown, to whose judgment all 



lightly of. No doubt he was an botanists defer, spoke highly of it 



enthusiast, and perliaps carried to me, and remarked that only 



some of his ideas to an extreme those who knew little of the bub- 



lengtli. But I feel sure, from my ject would laugh at him. 



