16 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



tions has proved most instructive, and another very 

 important method of investigation has been the power 

 of obtaining very thin slices by imbedding the object 

 to be examined in paraffin or some other soft substance. 

 In this manner we can now obtain, say, fifty separate 

 sections of the egg of a beetle, or the brain of a bee. 



At the close of the last century, Sprengel published 

 a most suggestive work on flowers, in which he pointed 

 out the curious relation existing between these and 

 insects, and showed that the latter carry the pollen 

 from flower to flower. His observations, however, 

 attracted little notice until Darwin called attention to 

 the subject in 1862. It had long been known that the 

 cowslip and primrose exist under two forms, about 

 equally numerous, and differing from one another in 

 the arrangements of their stamens and pistils ; the one 

 form having the stamens on the summit of the flower 

 and the stigma half-way down ; while in the other the 

 relative positions are reversed, the stigma being at the 

 summit of the tube and the stamens half-way down. 

 This difference had, however, been regarded as a case of 

 mere variability ; but Darwin showed it to be a beauti- 

 ful provision, the result of which is that insects fertilise 

 each flower with pollen brought from a different plant ; 

 and he proved that flowers fertilised with pollen from 

 the other form yield more seed than if fertilised with 

 pollen of the same form, even if taken from a different 

 plant. 



Attention having been thus directed to the question, 

 an astonishing variety of most beautiful contrivances 

 have been observed and described by many botanists, 

 especially Hooker, Axel, Delpino, Hildebrand, Bennett, 



