60 HISTORY OF BOTANY 



the double wall and the sculpturing on the exterior, 

 rather a feat when one considers the imperfect state of 

 the microscope in his day. He noticed that something 

 escaped from the pollen grain after it had lain for some time 

 on the stigma, and fancied that this something was an oil 

 which united with another oil secreted by the stigma, and 

 that the combined fluids passed down the style to the 

 ovary and there induced the formation of the embryo. 

 In another direction also Koelreuter achieved considerable 

 success. He tried the effect of artificially pollinating the 

 stigma of one flower with the pollen of another species, 

 and soon established the prepotency of the pollen taken 

 from other flowers of the same species. He was successful 

 also in obtaining hybrids between plants of different 

 species, and thus in driving the first nail into the coffin of 

 the dogma of the constancy of species. 



The real connection, however, between floral 

 morphology and insect visitation was discovered by 

 Conrad Sprengel, who, in 1795, published his observations 

 and deductions in a book whose title reflects the self- 

 gratification of its author in the results he had achieved 

 Das entdeckte Geheimnis der Natur im Bau und in der 

 Befruchtung der Blumen. Sprengel's main thesis is that 

 the structure of the flower can be interpreted only by 

 considering the duty of each part in relation to the visits 

 of insects. The colour and scent are the sign-boards 

 held out to attract the visitor's attention ; the markings 

 on the corolla are guides showing the way to the hidden 

 nectar supplies, like the indicative hands at our shop 

 doors labelled " Jones's only entrance." Sprengel goes 

 on to describe the various adaptations for the protection 

 of nectar, and points out how hairs and scales shield it 

 from rain, " just as a drop of sweat falling down a man's 

 brow is stopped by the eyebrow and eyelash and hindered 

 from running into the eye. . . . Insects can easily 

 reach it but the rain cannot spoil it." Sprengel draws 

 attention also to the order of ripening of stamens and 



