A MANUAL OF BOTANY 101 



cell with parts of those adjacent {h[)) ; (4) same as (3), but 

 stained with iodine; (5) an end cell {Jp) ; (G) cells of other 

 species of spirogyra; (7) conjugating spirogyra (Jp) and 

 oospores {hp) ; (8) filament after application of salt solu- 

 tion ; (9) cell division (if observed) (Ip). 



Cell division. In spirogyra that is fresh and bright green, 

 try to discover in the same filament lonrj and short cells. 

 How could you obtain the short cells from the long 

 ones ? If you find such a condition, it means the repro- 

 duction of the filament by vegetation, multiplication, or cell 

 division. In this method how could a single filament, in 

 time, fill a small si)ring or pool ? 



Experiments. To fresh living s[)irogyra, temporarily 

 mounted, add strong solutions of sugar or salt, and observe 

 the effect on the chloroplast band and other cell contents. 

 An action called plasmolysis is taking place; read about 

 this in reference books. 



Examine material growing in bright sunlight. Try to 

 perfect some plan for obtaining the gas thrown off. (In- 

 structor may arrange experiment, with the idea of determin- 

 ing the nature.) The plant is making food from the minerals 

 in the water by means of its chlorophyll-stained cytoplasm, 

 the sunlight being the direct stimulus. The gas thrown 

 off is waste matter (to the plant in this process) and is, 

 at least in large part, oxygen. The process is called 7>/io?o- 

 synthesis, which is the food-making process of all chlorophyll 

 plants. 



Problems. 1. What effect would this alga have on the 

 purity of pond water ? What benefits would come to the 

 animals living in such water ? 



2. Why does it grow in relatively quiet waters ? 



3. Why does it not grow in the ocean ? 



4. Why is it not a good plant for the aquaria ? 



5. Why is it often called "brook silk " ? 



6. Why does it make starch '* 



