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. 
