158 SYSTEMATIC BOTANY. 



PART II, 



SYSTEMATIC BOTANY, 



CHAPTER I. 



PRINCIPLES OF CLASSIFICATION. 

 Sect. 1. SPECIES AND GTENEKA. 



Systems of Classification. In throwing plants together into 

 groups, two methods may be adopted, constituting respectively an 

 artificial or a natural system of classification. In the former, the 

 only object is to arrange or place objects in such order that we may 

 find them readily by some prominent mark, in the same manner as 

 words are arranged alphabetically in a dictionary. In a Natural 

 Classification, the object is so to combine our materials that the 

 things brought closest together shall have the greatest possible 

 agreement; from which it results that a knowledge of ail the 

 peculiarities of one carries with it the knowledge of most of those 

 of its neighbours, and enables us, from the observation of a portion 

 of the characters of a given kind, to foresee the rest. According 

 to the derivative theory a group is natural in proportion to the 

 accuracy with which it expresses the degree of relationship of the 

 members of the group to each other, and of one group to its fel- 

 lows. If there is no real kinship the resemblance is only super- 

 ficial, and the classification therefore artificial. 



Species. Systematic Botany is founded upon the real or assumed 

 existence of distinct kinds or species of plants a notion which 

 of course belongs not to science exclusively, but is a part of the 

 common experience of the world. But there is a great difference, 

 practically, between the kinds of things accepted in the ordinary 

 affairs of life and the kinds admitted in science, more especially in 

 the Biological sciences. 



