172 Introduction to Botany. 



means of wind, insects, etc., the beneficial effects of this 

 process, so definitely determined by the experiments of 

 Darwin, were evidently unsuspected by him. 



125. SprengePs Discoveries. — Sprengel's book, entitled 

 "The Discovered Secret of Nature in the Structure and 

 Fertilization of Flowers " (Berlin, 1793), is of great inter- 

 est to the student of botany, not only because it contains 

 an exposition of many important discoveries, but also be- 

 cause it reveals an inquiring and unprejudiced mind, capa- 

 ble of placing facts in their true relationships, and of 

 understanding their meaning. A few paragraphs from 

 Sprengel's book are here given as an illustration of his 

 method of reasoning. 



"While in the summer of 1787 I was attentively examin- 

 ing the flower of Geraniuui sylvaticiini, I found that the 

 lowest part of its petals was provided on the inside and 

 on the two borders with fine and delicate hairs. Persuaded 

 that the wise Author of nature has not created even a 

 single hair without a definite object, I considered what 

 purpose these hairs might possibly serve. And in this 

 it soon occurred to me that if one assume that the five 

 drops of nectar, which are secreted by the same number of 

 glands, are set aside for the food of certain insects, one 

 would then not find it improbable that provision should be 

 made to preserve this nectar from injury by rains, and that 

 these hairs had been placed there for this purpose. . . . 



"Each drop of nectar sits upon its gland immediately 

 under the hairs which occur on the borders of the two 

 adjacent petals. Since the flower stands upright and is 

 rather large, raindrops necessarily fafl into it when it rains. 

 But none of the faUing raindrops can reach a droplet of 

 nectar and mix with it, since it is held back by the hairs 

 which occur over the droplet of nectar, just as a drop of 



