Elementary Species in Nature 33 



as to what groups are real units and will remain 

 constant and unchanged through all the years 

 of our observations. 



Before Linnaeus, the genera were the real 

 units of the system. De CandoUe pointed out 

 that the old common names of plants, such as 

 roses and clover, poplars and oaks, nearly all 

 refer to genera. The type of the clovers is 

 rich in color, and the shape of the flower-heads 

 and the single flowers escape ordinary obser- 

 vation; but notwithstanding this, clovers are 

 easily recognized, even if new types come to 

 hand. White and red clovers and many other 

 species are distinguished simply by adjectives, 

 the generic name remaining the same for all. 



Tournefort, who lived in the second half of 

 the 17th century (1656-1708), is generally con- 

 sidered as the author of genera in systematic 

 botany. He adopted, what was at that time 

 the general conception and applied it through- 

 out the vegetable kingdom. He grouped the 

 new and the rare and the previously over- 

 looked forms in the same manner in which the 

 more conspicuous plants were already ar- 

 ranged by universal consent. Species were dis- 

 tinguished by minor marks and often indicated 

 by short descriptions, but they were consid- 

 ered of secondary importance. 



Based on the idea of a direct creation of all 



