PROTOPLASM, AN ACTIVE SUBSTANCE 29 



By slowly changing the focus you will be able to see that the Elodea leaf 

 is made of more than one layer of cells. 



I. What striking difference do you observe between Elodea and onion 

 cells ? 



II. Describe the new structures that vou observe in Elodea cells. These 

 are called chloroplasts or green color bearers. 



III. Observe two conspicuous differences between the chloroplasts and the 

 rest of the cytoplasm. 



IV. Trace the movement of the chloroplasts. Do they move around in 

 the individual cells or do they pass from cell to cell ? Suggest a reason for 

 your answer. The chloroplasts are carried by the movement of the stream- 

 ing protoplasm. 



V. Remove the cover glass, add a drop of dilute iodine, re-cover, and 

 mount again. 



VI. Describe the structures you now observe, that were also present in the 

 onion cell. 



VII. Make a diagram, times five, of a few of the cells of the Elodea. By 

 means of arrows, trace the pathway of the moving chloroplasts. Label cell 

 wall, cytoplasm, nucleus, vacuole, chloroplast. 



Protoplasm, an active substance. The movement of protoplasm, 

 observed by you in Elodea, was first observed by Von Mohl. He 

 recognized that the living, streaming, moving protoplasm was the 

 cause of the motion that we observed in our Elodea cells. 



Another name should be added to the list of those who devoted 

 a large amount of their time to the study of the cell. Max 

 Schultze, a German anatomist, in 1863, clearly brought out the 

 fact that protoplasm (nucleoplasm and cytoplasm) is the unit of 

 all physiological activities. Before his time, people thought that 

 plant cells were made of one kind of living material and animal 

 cells of another kind. Much has been added to the work of 

 Schultze, but many of the facts discussed in the following para- 

 graph are largely a result of his efforts. 



The key to every biological problem is sought in the cell ; for 

 every living organism is, or at some time has been, a cell. As 



