CHAPTER XIII 

 THE GREAT GROUPS OF PLANTS 



165. The entire question of taxonomic groups is very 

 difficult and intricate, and there is at present a consider- 

 able difference in opinion and usage, even among those 

 equally competent to judge. As set forth in Chapter IX, 

 the segregation and sequence of larger groups may be 

 based chiefly upon the morphology of living plants, or 

 upon that basis supplemented by the findings of anatomy 

 (including embryology and histology), comparative life 

 histories, and paleobotany.^ Manuals and "Floras" of 

 systematic botany are, for the most part, arranged upon 

 the former basis, which operates at present in the direction 

 of conservatism and few changes in connection with the 

 largest groups, or phyla. Regard for the evidence from 

 other sources is more apt to result in conflict of opinion and 

 more frequent revisions in the light of new studies, but it 

 is also more apt to result in a closer approximation to the 

 truth. In the former case the sequence of groups is 

 chiefly based upon complexity of organization, proceeding 

 from the simpler to the more complex. On this basis the 

 monocotyledons, for example, would precede the dicotyle- 

 dons, the order observed in the Manuals. 



In the latter case the sequence of groups attempts to 

 indicate or reflect their order of development in time, as 

 indicated by the data of paleobotany, comparative life- 

 histories, comparative anatomy, and plant geography. 

 On this basis the monocotyledons would follow the 



'See, also, p. 236. 



243 



