THE BASIS OF PLANT CLASSIFICATION 



39 



two are generally recognized — the plants and the animals — and even they 

 cannot be sharply separated from each other, for the simplest plants and the 

 lowest animals differ but little. 



Every species, genus, family and so on is defined botanically by what 

 is called a diagnosis, generally written, for the sake of precision, in Latin, 



Fig. 19. — Erophila verna. A number of micro species 

 included in the Linnean species. {After Jordan.) 



giving in general terms a description of the characters common to the organ- 

 isms or groups of organisms which are to be included in the assemblage, 

 and no additional individual or group can be included unless it conforms to 

 the diagnosis of the group into which it is placed. 



The arrangement of individual organisms into species, and the 

 grouping of these into genera, families and so on, constitutes the work of 

 the systematist, and is usually spoken of as classification ; whilst the 

 study of the principles in accordance with which the classification should 

 be carried out forms the special branch of biology spoken of as taxonomy. 



History of Cl.\ssific.\tion 



The history of classification was for many centuries the history of Botany. 

 The earliest interest of man in plants was entirely in their usefulness to him, 



