PHYSIOLOGY. 



Protoplasm in spirogyra. 



4. The plant spirogyra. This plant 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 sometimes given 

 to this plant, along with others which are more or less closely 

 related. It is an alga, and belongs to a group of plants known 

 as alga. 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 con- 

 tained in one of these floating mats is very great. 



Let us place a bit of this thread tangle on a glass slip, and 

 examine with the microscope and we will see certain things about 

 the plant which are peculiar to it, and which enable us to dis- 

 tinguish it from other minute green water plants. We shall 

 also wish to learn what these peculiar parts of the plant are, in 

 order to demonstrate the protoplasm in the plant.* 



5. Chlorophyll bands in spirogyra. We first observe the 

 presence of bands ; green in color, the edges of which are 

 usually very irregularly notched. These bands course along in 

 a spiral manner near the surface of the thread. There may be 

 one or several of these spirals, according to the species which 

 we happen to select for study. This green coloring matter of 

 the band is chlorophyll, and this substance, which also occurs in 

 the higher green plants, will be considered in a later chapter. 

 At quite regular intervals in the chlorophyll band are small 

 starch grains, grouped in a rounded mass enclosing a minute 

 body, the pyrenoid, which is peculiar to many algae. 



6. The spirogyra thread consists of cylindrical cells end to 

 end. Another thing which attracts our attention, as we examine 

 a thread of spirogyra under the microscope, is that the thread is 



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

 pairs, and connected with short tubes. In some of the cells there will be 

 found rounded or oval bodies known as zygospores. These may be seen in 

 fig. 86, and will be described in another part of the book. 



