PLANTS AND ANIMALS 



223 



hydrous membranes stretch but little, while 

 nitrogenous membranes are highly extensible; 

 and herein lies the basis of the wonderful di- 

 vergence in mobilit^^ shown b^^ animals and 

 plants. The power of free movement, which 

 characterizes the animal and has rendered 

 possible its great and varied development, 

 depends primarily upon the nature of the in- 

 vestment, just as the rigidity of plant bodies 

 and their slow adjustments also depend by 

 restriction upon the investment. It is no 

 doubt possible in ultimate analysis to trace 

 man3^ of the 

 prominent phy- 

 siological char- 

 acters of both 

 kingdoms to 

 this difference 

 in structure. 



In applying 

 the crucial test, 

 some organ- 

 isms present 

 special difficult- 

 ies. Some forms 

 in their vegeta- 



Fig. 25. — A mycetozoan in its vegeta- 

 tive or Plasmodia! state, much magni- 

 fied. (After Cienkowski.) 



tive state con- 

 sist of so-called 

 naked protoplasm, of which themostcon 



The test 

 applied 



