CHAPTER IV. 

 THE LIVING SUBSTANCE OF PLANTS— Continued. 



II. Protoplasm in an Alga: Spirogyra. 



39. The plant spirogyra.* — There are a number of algse 

 which would serve the purpose quite as well as spirogyra, but 

 we shall want to employ this plant again at a later time, and 

 it is well now to become familiar with it. It is found in the 

 water of pools, ditches, ponds, or in streams of slow-running 

 water. It is green in color, and occurs in loose mats, usually 

 floating near the surface. The name " pond scum " is some- 

 times given to this plant, along with others which are more or 

 less closely related. If we lift a portion of it from the water, 

 we see that the mat is made up of a great tangle of green silky 

 threads. Each one of these threads is a plant, so that the 

 number contained in one of these floating mats is very great. 



Demonstration 6. 



40. To prepare spirogyra for study under the microscope. — Lift up a bit of 



this thread tangle with a needle and place it in a drop of water on a " glass 



slip." With the needles tease apart the threads so that they will be scattered 



in the water. Now place over these threads in the water a clean, thin, glass 



circle. Place the preparation on the stage of the microscope and adjust for 



observation of a thread. Let the pupils first examine the plant under the 



low power of the microscope, and then under the high power. They should 



e 



* If spirogyra is in fruit some of the threads will be lying parallel in pairs, 



and connected by short tubes. In some of the cells may be found rounded or 



oval bodies known as zygospores. These may be seen in figure 93 and will 



be described in another part of the book. 



19 



