Chap. IX. CONCLUDING REMARKS. 275 



compelling- insects to visit the flowers in front. Few 

 persons now doubt the correctness of C, K. Sprengel'* 

 view,* that the bright and conspicuous colours oi 

 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 tlie 

 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 stands in front of the rostellum, 

 and its outer portion often serves as a landing-place 

 for the necessary visitors. In Epipadis palustris 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 



* Tliia author's curious work, owu observations, that his work 

 with it.-i quaint titlt; of ' Das Eiit- contains an immense boily of 

 .k'ckte Geheimniss der Natnr,' truth. Many years ago Robert 

 until latu'ly was often spokcui Brown, to whose judgment all 

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

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

 B >me of his ideas to an extreme those who knew little of the sub- 

 length. But I feel sure, from uiy jcct wculd laugh at him. 



T 2 



