22 



EXPERIMENTAL GENERAL PHYSIOLOGY 



these low organisms takes place by what is called fission. This process 

 is a simple division of the cell body into two equal portions. The 



FIG. 1 



a, Desmids. Common forms. Shaded portions of green chlorophyll, outer envelope of cellu- 

 lose, b, Protococcus. Common forms, showing reproduction. A cellulose envelope enclosing 

 chlorophyll. 



first undivided cell is called the "mother cell" or the adult cell, 

 while the two young cells resulting from the fission are called 

 "daughter cells." 



FIG. 2 



n 'Cy Ch s 



Spirogyra, Two cells of a long fibre are shown : w, cellulose cell wall; n, nucleus surrounded 

 by cytoplasm (Cy), which sends out threads to the cell wall; Ch, chlorophyll band making two 

 and one-half spiral turns around the inside of the cell wall; s, starch grain surrounded by sev- 

 eral oil globules. 



Spirogyra. This plant occurs in long, delicate threads which 

 represent numerous cylindrical cells joined end to end. It receives 

 its name from the spiral disposition of its chlorophyll. Each cell 

 posesses two or three or four threads of chlorophyll, which are wound 



