Vlll PREFACE. 



also to the substantive terms explained in Organo- 

 graphy, will be found in a copious index at the end of 

 the volume. 



These topics exhaust the science considered only 

 with reference to first principles ; there are, however, 

 a few others which it has been thought advisable to 

 append, on account of their practical value. These 

 are, firstly, Phytography (Book IV.) j or, an ex- 

 position of the rules to be observed in describing and 

 naming plants. As the great object of descriptions 

 in natural history, is to enable every person to recog- 

 nise a known species, after its station has been dis- 

 covered by classification, and also to put those who 

 have not had the opportunity of examining a plant 

 themselves into possession of all the facts necessary 

 to acquire a just notion of its structure and affinities ; 

 it is indispensable that the principles of making 

 descriptions should be clearly understood, both to 

 prevent their being too general to answer the intended 

 purpose, or more prolix than is really requisite. It 

 is the want of a knowledge of these rules that renders 

 the short descriptions of the classical writers of an- 

 tiquity, and the longer ones of many a modern tra- 

 veller, equally vague and unintelligible. In this 

 j)lace are inserted a few notes upon the formation of 

 an herbarium. 



After this, has been introduced (Book V.) a sum- 

 mary of the little which is known of the laws that 

 regulate the distribution of plants upon the surface of 

 tiie earth ; a question which, however indefinite and 

 unsatisfactory our information may at present be, has 

 begun to assume such an appearance as to justify the 

 expectation, tliat future discoveries will explain the 

 causes of the characters of vegetation being deter- 

 mined, as they surely are, by climate. 



