THE LIVING SUBSTANCE OF PLANTS. 



21 



the axis of the cell in some species; or triangular, 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 star-like manner, and terminate in the 

 chlorophyll band by one of the groups cf starch grains. 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. 



44. Cell-sap in spirogyra. The greater part of the interior 

 space of the cell, that between the radiating strands of proto- 

 plasm, is occupied by a watery fluid, the " cell-sap." 



Demonstration 7. 



45. Test for protoplasm in spirogyra. Mount a few threads of spirogyra 

 in a drop of weak solution of iodine for microscopic examination. 



Fig. 9. 



Cell of spirogyra before treat- 

 ment with iodine. 



Fig. io. 



Cell of spirogyra after treatment 

 with iodine. 



The iodine gives a yellowish-brown color to the protoplasm, 

 and it can be more distinctly seen. The nucleus is also much 

 more prominent since it colors deeply, and we can perceive 

 within the nucleus one small rounded body, sometimes more, 



