OUTLINE OF CLASSIFICATION 227 



359. General outline of classification. In the study of the 

 representatives of the different subkingdoms the limits of this 

 work will permit the discussion of but a few. It may be con- 

 venient to precede this study with a brief outline of a general 

 classification including the divisions of a higher grade, since it is 

 only the more general features of morphology and relationship 

 which come within the scope of this work. 



To the teacher. It is impossible to arrange the groups of 

 plants in a linear sequence which would represent the line of 

 their development from the simpler or lower plants to the more 

 complex or higher ones. Each group includes simple and com- 

 plex forms. Very often the complex or higher forms of one group 

 are more complex than all the forms of another group, but the 

 lower forms of the former may be simpler than the lower forms 

 of the latter. For example, in the algae, the blue-green algae 

 (Cyanophycece) as a whole are simpler than the green algae 

 (Chlorophycea) , because the latter have advanced in the more 

 complex forms to a much higher stage of development, but the 

 simpler green algae are simpler and lower than any of the blue- 

 greens, which appear to be a very peculiar group and certain of 

 their structural characters are not well known. In studying 

 groups of plants, therefore (as well as of animals), it is more 

 satisfactory to study the groups much as one would read the 

 different chapters of a book which deals with related events in 

 each chapter, though the succession of chapters might not repre- 

 sent a succession in time. For example, in studying history, 

 we do not usually cover the world's history for one year before we 

 pass on to the next year, but we study American history, English 

 history, Roman history, etc. To illustrate this as applied to the 

 algae, the different classes (with perhaps the exception of the 

 Charophycece, which are a high and specialized group) are all 

 supposed to have had their origin in a large and very simple 

 group of organisms, and then each group developed along an 

 independent line which might be represented by the following 

 diagram: 



