SPRENGEL AND FERTILISATION OF FLOWERS 91 



induced to seek for the store of honey within. He 

 tested his conjecture by examining- other honey-bearing 

 flowers, and soon collected many instances of spots, 

 lines, folds, and ridges, which might not only make 

 insects aware of hidden stores of honey, but guide them 

 to the exact place. Contrivances of the most diverse 

 kinds, but all tending- to invite the visits of insects and 

 utilise them for the benefit of the plant, rewarded 

 Sprengel's continued inquiries. He found that night- 

 flowering plants, which could derive no advantage 

 from coloured patterns, often have larg-e white corollas, 

 easily discerned in a faint light, and that these flowers 

 give out an odour attractive to nocturnal insects. He 

 found that the pollen-masses of an orchis are actually 

 removed by larg-e insects, though here no honey could 

 be detected in the flower. Sprengel's fertility in 

 probable conjecture is shown by his explanation of this 

 puzzling case ; he sugg-ested that the orchis is a sham 

 honey-bearer (Scheinsaftblume), which attracts insects 

 by assuming the conspicuous size and coloration found 

 in most honied flowers. Darwin suspected, and 

 Herman Muller proved, that though the spur of the 

 orchis-flower is empty, it yields when pierced a fluid 

 attractive to bees and other insects. Spreng-el dis- 

 covered too how insects g-et imprisoned in the corolla 

 of an Aristolochia, whose reflexed hairs allow small 

 flies to creep in, but effectually prevent their escape 

 until they have fertilised the pistils, when the hairs 

 relax. These are only specimens of a multitude of 

 adaptations which fill the book. 



Sprengel insists upon the study of flowers under 

 natural conditions ; he could never have made out by 

 the examination of plucked flowers how Nig-ella is 

 fertilised. Flies with attached pollen-masses, which he 



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