﻿PLANTS AND ANIMALvS 



hydrous membranes stretch but little, while 

 nitrogenous membranes are highly extensible; 

 and herein lies the basis of the wonderful di- 

 vergence in mobility shown by 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 

 many 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- 

 tive state con- 

 sist of so-called 

 naked protoplasm, of which themostcon 



# 



-:> 



Fig. 25. — A mycetozoan in its 

 tive or plasmodial state, much 

 fied. (After Cienkowski.) 



egeta- 

 nagui- 



Thc test 

 applied 



