CHAPTER IV. 

 THE PLANT-BODY. 



109. Generalized Forms. — The cells, tissues, and tissue- 

 systems described in the preceding pages are variously ar- 

 ranged in the different groups of the vegetable kingdom 

 to form the Plant-Body. The simplest plants are single 

 cells or masses of similar cells; in those next higher the 

 cells are aggregated into a few simple tissues; while still 

 above these the tissues are grouped into tissue-systems. 



110. With this internal differentiation there is a corre- 

 sponding differentiation of the external plant-body. The 

 lower plants are not only simpler as to their internal struc- 

 ture, but they are so as to their external form as well. 

 The higher plants are as much more complex than the lower 

 ones as to their external parts as they are in regard to their 

 tissues and tissue-systems. 



111. In the lowest groups of plants the simple plant-body 

 has no members; the single- or few-celled seaweed has no 

 parts like root, stem, or leaf; it is a unit as to its external 

 form. In the higher groups, on the contrary, the plant- 

 body is composed of several or many members which are 

 less or more distinct. In those plants in which they first 

 appear, the members are not clearly or certainly to be dis- 

 tinguished from the general plant-body; but in the higher 

 groups they become distinctly set off, and are eventually 

 differentiated into a multitude of structural and functional 

 forms. 



