THE BOOTS 53 



instances, and absorption is carried on by the entire 

 body. Some of these organisms accomplish fixation 

 in certain stages of their existence by means of jelly- 

 like substances outside their walls. Some of these 

 floating forms run out minute threads of protoplasm, 

 with which they lash the water in such manner as 

 to swim from place to place. Others, with single 

 or many celled bodies, make holdfasts, or fixing 

 roots, with which they attach themselves to the 

 rocks or the bottom of the pond or stream. 



A general idea of the nature of these organisms 

 may be gained by an examination of the pond-scums 

 {Sjjirogyra), which float near the surface, and are 

 made up of a number of long threads, each thread 

 being formed by the division and growth of num- 

 bers of rod-shaped green cells. 



