insect trfsftors. 215 



rain, that the insects may get it pure and un- 

 defiled. 



2. The colors and odors of flowers are de- 

 signed to attract the attention of insects. 



3. Without the aid of insects very many 

 flowers are incapable of fertilization, and there- 

 fore the secretion of honey in the flower, its pro- 

 tection, the odor of the flower, and the coloring 

 of the corolla, are Nature's contrivances to cause 

 its fertilization by insects. 



While bringing forward the fact, however, 

 that the pollen was conveyed by insects to the 

 stigma, no greater advantage was assigned by 

 Sprengel than direct contact of the reproductive 

 organs in itself no advantage over natural fer- 

 tilization without suspecting that the real value 

 of insect-visits to the plant consisted in the pol- 

 len being thus carried to the stigmas of other 

 flowers, and by this means accomplishing cross- 

 fertilization. So, Sprengel's work, " The Se- 

 cret of Nature in the Form and Fertilization of 

 Flowers discovered," was allowed to lie fallow 

 until called up again by the advance of knowl- 

 edge and the researches of modern scientists, 

 more particularly by Darwin's great work, " The 

 Origin of Species," and his later book, " The Fer- 

 tilization of Orchids." Miiller's work, published 

 much later than those of Darwin, besides the 



