LABORATORY AND FIELD WORK 399 



CHAPTER V 



1. Examine a mass of Spirogyra growing on the surface of a jar 

 of water in bright sunlight. How do the plants feel to the touch ? 

 What is their color? Notice the bubbles of gas tangled among 

 the plants. 



2. Compare a similar culture which has been kept in the dark 

 for at least twelve hours. Are the plants on the surface of the 

 water, or at the bottom ? Why ? Do the plants differ in appear- 

 ance in any way from those that have stood in the light ? 



3. Disentangle from the mass a single thread-like plant or as 

 large a part of one as possible. How long is the thread? Is it 

 branched ? 



4. Examine a plant under the microscope. Notice that it is 

 made up of cells joined end to end. Are the cells alike in length ? 

 In thickness ? What is the shape of a cell ? 



6. Study a single cell, noting the parts mentioned below. Some 

 of these parts can be seen more clearly if the plant is placed for a 

 short time in a weak solution of iodine in potassium iodid. This 

 kills the living materials of the cell and stains them yellowish- 

 brown. However, the cell should first be studied while alive, and 

 everything possible observed in the living condition. 



a. The outer wall. 



b. The cross wall between two adjoining cells ; compare this with the 



outer wall. 



c. The layer of slimy cytoplasm, containing granules. Is it in 



motion ? 



d. The green chloroplast or chloroplasts. What is the shape of one ? 



Can you trace it from one end of the cell to the other ? Where 

 does it lie with reference to the wall ? Where does it lie with 

 reference to the slimy cytoplasm ? 



e. Colorless bodies (pyrenoids) imbedded in the chloroplast. In the 



iodine solution a blue or blue-black color will appear just outside 

 each pyrenoid ; if the iodine acts long enough, the color may 

 become so dense that the pyrenoid itself appears to be stained. 

 What is the meaning of this blue color ? 



/. The nucleus, a rather dense spherical or ellipsoidal body at or 

 near the center of the cell ; it contains a globular, somewhat 

 brighter body, the nucleole. 



