Chap, i.] Joseph G. Koelreuter and Konrad Sprengel. 41 ; 



to the further conclusion : ■ If the corolla has a particular 

 colour in particular spots on account of the insects, it is fur 

 the sake of the insects that it is so coloured ; and if the 

 particular colour of a part of the corolla serves to show an 

 insect which has lighted on the flower the direct path to the 

 juice, the general colour of the corolla has been given to it, in 

 order that insects flying about in search of their food may see 

 the flowers that are provided with such a corolla from a long 

 distance, and know them for receptacles of juice.' 



He afterwards discovered that the stigmas of a species of 

 Iris were absolutely unable to be fertilised in any other way 

 than by insects, and further observation convinced him more 

 and more, ' that many, perhaps all flowers, which have this 

 juice, are fertilised by the insects which feed on it, and that 

 consequently this feeding of insects is in respect of themselves 

 an end, but in respect of the flowers only a means, but at the 

 same time the sole means to a definite end, namely, their 

 fertilisation ; and that the whole structure of such flowers can 

 be explained, if in examining them we keep in sight the fol- 

 lowing points, first, that flowers were intended to be fertilised 

 by the agency of one or another kind of insects, or by several ; 

 secondly, that insects in seeking the juice of flowers, and for 

 this purpose either alighting upon them in an indefinite 

 manner, or in a definite manner either creeping into them or 

 moving round upon them, were intended to sweep off the dust 

 from the anthers with their usually hairy bodies or with some 

 part of them, and convey it to the stigma, which is provided 

 either with short and delicate hairs, or with a viscid moisture, 

 that it may retain the pollen.' 



In the summer of 1790 he detected dichogamy, which he 

 first observed in Epilobium angustifolium. He found, ' that 

 these hermaphrodite flowers are fertilised by the humble-bee 

 and by other bees, and that the individual flower is not fer- 

 tilised by its own pollen, but the older flowers by the pollen 

 which the insects convey to them from the younger.' Having 



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