Flowers. 171 



greater value of the sexual as compared with the asexual 

 method of reproduction becomes apparent. 



124. Historical Summary. It appears from the writ- 

 ings of Aristotle and Theophrastus (about 350 B.C.) that 

 only vague notions were entertained at that time about the 

 essential nature of flowers. It was a common practice of 

 the palm culturists of that time to shake the branches of 

 the staminate trees over the flowers of the pistillate trees 

 (see page 175 for definition of staminate and pistillate), in 

 order to- increase the production of fruit, and Theophrastus 

 remarks that there was obviously a great difference in the 

 flowers ; but he seems not to have attempted to find out 

 wherein the difference consisted. As late as A.D. 60 Pliny 

 writes,. in speaking of the date palm, that the pollen dust 

 is the material of fertilization, and that naturalists say all 

 trees and even herbs have the two sexes, but knowledge of 

 the subject was at that time indefinite and conjectural. It 

 was Camerarius (1665-1721) who was the first to show by 

 definite experiment that the cooperation of the pollen is 

 necessary to the formation of an embryo within the ovule. 



Koelreuter (1733-1806) observed the nectar and noted 

 the aid of insects in pollination ; and he produced hybrids 

 by the transference of the pollen of one species to the 

 stigmas of the flowers of another species. Conrad 

 Sprengel (1750-1816) noted that cross fertilization between 

 different flowers and between flowers of different individ- 

 uals was of common occurrence in nature, and he said that, 

 judging from the construction of flowers, nature seemed to 

 have intended that no flowers should be fertilized by their 

 own pollen ; and he concluded further that the various 

 peculiarities of structure in flowers have a definite relation 

 to insects in effecting pollination. While Sprengel dis- 

 covered the common occurrence of cross fertilization by 



