CHAPTEK IV. 



THE PLANT-BODY. 



111. Diflferentiation of the Plant-body. — The cells, tis- 

 sues, and tissue-systems described in the preceding pages 

 are variously arranged in the different groups of the vege- 

 table kingdom to form the Plant-hody . 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. 



112. With this internal differentiation there is a corre- 

 sponding difEerentiation 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. 



113. Members of the Plant-body. — In the lowest groups 

 of plants the simple plant-body has no members; the sin- 

 gle- 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 distinguished from the genera] 



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