98 TAXONOMY. 



tion of the same plant during its different ages, and amidst 

 the most different circumstances which have an influence on 

 it. When, for instance, in the common Lotus corniculatus, 

 on whatever soil it may grow, we uniformly observe that 

 it has a solid stem, even and erect divisions of the calyx, 

 and expanded filaments, we must of necessity distinguish, as 

 a particular species from it, another form which grows in 

 bogs and in watery meadows, which has a much higher, and 

 always hollow stalk, the divisions of its calyx spread out into 

 a star-shape and hairy, and which has uniformly thin fila- 

 ments; and we must name this latter species either Lotus 

 uUgmosus with Schkuhr, or Lotus major with Scopoli and 

 Smitli. As, on the other hand, the Pimpinella Sax'ifraga 

 grows sometimes quite smooth, and sometimes, in woods and 

 shady meadows, considerably hairy ; as it displays sometimes 

 simple and small stem-leaves^ sometimes half and even doub- 

 ly pinnated leaves ; and as these forms vai'y according to the 

 situation of the plant and during reproduction, we cannot 

 regard these forms by any means as distinct species, but we 

 must view them as corruptions. 



We see, that, in order to decide respecting the idea of a 

 species, an observation of many years, and of much accuracy, 

 is often required; and that the cultivation of plants, from 

 the most different climates, in botanical gardens, is in the 

 highest degree necessary for their discrimination. 



II. Idea of a Genus. 



147. 

 By a Genus we understand the sum of the species which 

 agree in certain constant properties of the essential parts. 

 When we compare several species of Roses vnXh one another, 

 we soon find that they have all certain common marks, and 

 that it is hence an easy matter for every person, who perceives 

 their sum of corresponding properties, to say that he has a 

 Rose before him. 



