CHAPTER X 

 THE GREAT GROUPS OF PLANTS 



142. The basis of classification. In the preceding chapters 

 little has been said about classifying plants into groups. 

 Practically all the plants discussed so far belong to one 

 group, and since flowers and seeds are characteristic structures 

 in these plants, the group is usually spoken of as the Flower- 

 ing or Seed Plants. Throughout the entire plant kingdom 

 one or more kinds of structures are generally used as the 

 basis for arranging plants into groups. What a plant may do 

 with these different structures, or where the plant lives, may 

 have some influence upon the classification of the plant, but 

 ordinarily these things all give way to considerations of struc- 

 ture in determining the group to which a plant belongs. 



It is true that such expressions as " desert plants," or 

 "parasitic plants," are used to group together plants that live 

 in certain kinds of regions, or that live by means of certain 

 processes, and such bases of classification are most interest- 

 ing and profitable ; but it has been found much more con- 

 venient and more satisfactory to arrange the great groups 

 upon the basis of structure and form. Beginners in botany 

 are often more interested in what plants are doing than in 

 what their structures are, but we must know what the struc- 

 tures are in order to understand what is being done. Also 

 a better degree of uniformity in classification is obtained by 

 using plant structures as its basis. 



143. The meaning of* genus and species. In most wooded 

 regions one or more kinds of oaks may be found. The follow- 

 ing kinds are common, and are known to many people who 

 have not studied botany : white oak, bur oak, red oak, black 

 oak, blackjack oak, live oak, and several other kinds. While 



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