INTRODUCTION. 129 



number of grasses agree in one or two particular 

 points, and differ therein from all the rest, such are 

 termed a genus or family. 



The differencejin the manner of inflorescence, and the 

 form of clothing of the culm, leaves, and roots, afford 

 the specific characters, or separate the genus into 

 species. When the difference between two grasses 

 amounts to little else than one or two of these last- 

 mentioned points, or when such distinctions are either 

 lost or found by raising the plant from seed, it is then 

 called a variety. 



These characters of genera, species, and varieties, 

 being founded on a few parts only, and those fre- 

 quently not very obvious, have been termed artificial 

 characters of distinction. The- memory, by these 

 means, is relieved from a multiplicity of minute dis- 

 tinctions, which would not be the case were all the 

 parts of the plant included in the essential specific 

 description or character. 



CHAPTER II. 



In the natural system of botany, plants are classi- 

 fied that is (in the language of Dr. Gray), "are 

 marshalled under their respective classes, orders, 

 tribes, genera, and species ; and they are character- 

 ized that is, their principal characteristics or dis- 

 tinguishing marks are described or enumerated, in 

 order that 1st, Their resemblances or differences, of 

 various degrees may be clearly exhibited, and all the 

 species and kinds ranked next to those they are most 

 related to ; and 2nd]y. That students may readily 

 ascertain the botanical names of the plants they meet 



