32 



THE HISTORY OF CELLS 



L Describe the cellular structure of a single strand of Spirogyra. When- 

 ever unicellular plants exist singly, end to end, the formation is called &, filament. 



In reality, each cell is a complete unit and 

 in no way dependent on the adjoining cells. 



II. Describe a struct lu^e in the cell that 

 suggests the reason for the name Spirogyra. 

 The name Spirog\Ta means coiling circles 

 {spira — coil; gyros — circle). What re- 

 semblance is there between a chloroplast of 

 Spirogyra and a chloroplast observed in the 

 Elodea? 



-c;^topla^TrL 

 -chloroplast 



-F>;^renoioL 



^ contaimng 

 cell Sap ^ 



I -cell xvocll 



- -filament- 

 ^hecttVL 



III. State the number of complete chlo- 

 roplasts observed in each cell of your 

 specimen. 



A. State the number of complete 

 turns found in each chloroplast. 



B. Using the words wavy, irregular, 

 or straight, describe the edge of the 

 chloroplast. 



IV. Identify the cell wall and the fila- 

 ment sheaths. This sheath is gelatinous 

 and gives the strands their characteristic 

 slimv texture. 



V. Draw a cell five times larger than 

 the one observed under the low power. 

 Show in your drawing how the adjoining 

 cells lie in relation to the one drawn. Label 

 cell wall, filament sheath, chloroplast. 



VI. Stain a cell with dilute iodine and focus under low power and then 

 imder high power. Locate and describe the nucleus, nucleolus, and strands 

 of cytoplasm. 



VII. Describe the location and suggest the nature of the contents of the 

 vacuoles left among the strands of cytoplasm. The part of the cytoplasm 

 inclosing the vacuoles is called the plasma membrane. 



VIII. Locate the structures stained blue. These are specialized cyto- 

 plasmic structures called pyrenoids. What evidence is present that the pyre- 

 noids make starch? 



Spirogyra is a single-celled plant. 

 These plants grow end to end and 

 thus form strands called filaments. 



