THE PLANT GROUPS 77 



SPIROGYRA (WATER SILK) 



1. Habitat and habit. Observe plants of the common green 



scum floating in an aquarium or on ponds in the open. 

 Eemove a small portion of the green mass to a watch 

 glass. Separate somewhat and examine with a hand 

 lens and the low power of a compound microscope. 



a. Is the green mass composed of one plant or many ? 



What is the nature of the Spirogyra plant ? Has it 

 roots, stems, or leaves? How does it differ from 

 plants of Protococcus ? 



b. Sketch one or two Spirogyra plants as seen under a 



low power. Name all structures observed. 



2. Cell structure. Study the cells of a Spirogyra plant under 



high power. Are the cells composing the plant all alike 

 or are they differentiated for different functions ? Note 

 the bandlike chloroplasts. How many are there in each 

 cell? 

 a. Chloroplast and pyrenoids. Compare fresh and stained 



plants of Spirogyra in the study of the pyrenoids. 



Read the text concerning the structure and function 



of the pyrenoids. 



(1) Stain fresh plants with iodine solution after they 



have been exposed to sunlight. Does the starch 

 sheath of the pyrenoid contain starch ? In what 

 part of the pyrenoid is the starch stored ? 



(2) Compare your specimen with a Spirogyra plant 



which has been specially stained and mounted 

 for study. Such preparations often show the 

 pyrenoids and nucleus with great distinctness. 



(3) Sketch a portion of a chloroplast and two or more 



pyrenoids greatly magnified. Indicate the starch 

 sheath and central granule of the pyrenoid and 

 the form and structure of the chloroplast. 



