PROTOPLASM. 



3 



made up of cylindrical segments or compartments placed end to 

 end. We can see a distinct separating line be- 

 tween the ends. Each one of these segments or 

 compartments of the thread is a cell, and the 

 boundary wall is in the form of a cylinder with 

 closed ends. 



7. Protoplasm. Having distinguished these 

 parts of the plant we can look for the protoplasm. 

 It occurs within the cells. It is colorless (i.e., 

 hyaline) and consequently requires close observa- 

 tion. Near the center of the cell can be seen a 

 rather dense granular body of an elliptical or 

 irregular form, with its long diameter transverse 

 to the axis of the cell in some species ; or trian- 

 gular, or quadrate in others. This is the nucleus. 

 Around the nucleus is a granular layer from which 

 delicate threads of a shiny granular substance 

 radiate in a starlike manner, and terminate in the 

 chlorophyll band at one of the pyrenoids. A 

 granular layer of the same substance lines the 

 inside of the cell wall, and can be seen through 

 the microscope if it is properly focussed. This 

 granular substance in the cell is protoplasm. 



8. Cell-sap in spirogyra. The greater part of 

 the interior space of the cell, that between the 

 radiating strands of protoplasm, is occupied by 

 a watery fluid, the " cell-sap." 



9. Reaction of protoplasm to certain reagents. 

 We can employ certain tests to demonstrate 

 that this granular substance which we have seen 

 is protoplasm, for it has been found, by repeated 



. . , J . , Thread of spiro- 



expenments with a great many kinds of plants, gym, showing lone 



. . cells, chlorophyll 



that protoplasm gives a definite reaction in re- band, nucleus, 



strands of proto- 



sponse to treatment with certain substances called plasm, and the 



granular wall layer 



reagents. Let us mount a few threads of the of protoplasm 

 spirogyra in a drop of a solution of iodine, and observe the 



