8 PHYSIO LOG Y. 



If we attempt to stain the living protoplasm with a one per 

 cent aqueous solution of eosin it resists it for a time, but if we 

 first kill the protoplasm with strong alcohol, it reacts quickly to 

 the application of the eosin. If we treat the living threads 

 with glycerine the protoplasm is contracted away from the wall, 

 as we found to be the case with spirogyra. While the color, 



Fig. 7. 

 Thread of mucor, showing protoplasm and vacuoles. 



form and structure of the plant mucor is different from spiro- 

 gyra, and the arrangement of the protoplasm within the plant 

 is also quite different, the reactions when treated by certain re- 

 agents are the same. We are justified then in concluding that 

 the two plants possess in common a substance which we call 

 protoplasm. 



Protoplasm in nitella. 



17. One of the most interesting plants for the study of one remarkable 

 peculiarity of protoplasm is Nitella. This plant belongs to a small group 

 known as stoneworts. They possess chlorophyll, and, while they are still 

 quite simple as compared with the higher plants, they are much higher in the 

 scale than spirogyra or mucor. 



18. Form of nitella. A common species of nitella is Nitella flexilis. 

 It grows in quiet pools of water. The plant consists of a main axis, in the 

 form of a cylinder. At quite regular intervals are whorls of several smaller 

 thread-like outgrowths, which, because of their position, are termed " leaves," 

 though they are not true leaves. These are branched in a characteristic fash- 

 ion at the tip. The main axis also branches, these branches arising in the axil 

 of a whorl, usually singly. The portions of the axis where the whorls arise 

 are the nodes. Each node is made up of a number of small cells definitely 

 arranged. The portion of the axis between two adjacent whorls is an inter- 



