SPIROGYRA 71 



Mount fresh filaments and study the chlorophyll bands, 

 or chloroplasts. What is their general form? How many 

 in a cell? How many spirals of the chloroplast in a single 

 cell? Note the form of the margin of the band. What 

 relation has ;this to certain round bodies, the pyrenoids, 

 situated at regular intervals along the bands? Test for 

 starch in the pyrenoids and surrounding granules. 



(c) Nucleus. Examine the cells in both fresh and stained 

 condition for the nucleus. Does it occupy the same position 

 in all cells ? What is its shape ? 



Make drawings to show the points observed. 



II. Physiology. 



1. Plasmolysis. In fresh specimens look for a very deli- 

 cate film of protoplasm lining the cell wall. If it cannot 

 be found in fresh specimens try the following experiment of 

 plasmolyzing the cell: Run a few drops of a 10 per cent 

 solution of salt or sugar under the cover glass, and note 

 what happens to the protoplasm. Is there any change in 

 the cell wall? In the chloroplast? During the experiment, 

 and probably before, vacuoles will have been noted in the 

 cells. What effect had plasmolysis upon these? Explain. 



2. Photosynthesis. Study the effects of light on starch 

 making by examining specimens which have been kept in 

 the dark for twenty-four hours and testing for starch. Com- 

 pare with specimens which have been freely exposed to light. 

 What conclusions may be drawn? 



3. Reproduction. Occasionally during the summer or 

 fall Spirogyra may be found in the process of conjugation. 

 This consists in the union of cells of two parallel filaments 

 lying close together by outgrowths of tubular processes 

 from each cell, and their final fusion with those of the adjacent 



