. BOTANY 



PART II. PLANT STRUCTURES 



CHAPTEE I 



INTRODUCTION 



1. Differences in structure. It is evident, even to the 

 casual observer, that plants differ very much in structure. 

 They differ not merely in form and size, but also in com- 

 plexity. Some plants are simple, others are complex, and 

 the former are regarded as of lower rank. 



Beginning with the simplest plants that is, those of 

 lowest rank one can pass by almost insensible grada- 

 tions to those of highest rank. At certain points in this 

 advance notable interruptions of the continuity are dis- 

 covered, structures, and hence certain habits of work, chang- 

 ing decidedly, and these breaks enable one to organize the 

 vast array of plants into groups. Some of the breaks ap- 

 pear to be more important than others, and opinions may 

 differ as to those of chief importance, but it is customary 

 to select three of them as indicating the division of the 

 plant kingdom into four great groups. 



2. The great groups. The four great groups may be 

 indicated here, but it must be remembered that their names 

 mean nothing until plants representing them have been 

 studied. It will be noticed that all the names have the 



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