GREEN PLANTS 1 



A. Pleurococcus 



1. Examine, with the dissecting microscope, the greenish material 

 present on the outside surface of a piece of bark and note its general 

 appearance. Scrape off a little of the material and place on a slide. 

 Mount in a drop of water and examine with the low power of the com- 

 pound microscope. Note that the material consists of great numbers of 

 tiny green, spherical bodies. Each of these is a cell, and each also con- 

 stitutes the entire plant body of this unicellular plant, Pleurococcus. 



2. Examine the preparation with the high power. Select a large single 

 cell and note : (a) the cell wall, which is quite thick and composed of 

 cellulose, and (b) the large green chloroplastid, which almost fills the body 

 of the cell and lies embedded in (c) the cytoplasm, (d) The nucleus lies 

 near the center of the cell but is usually more or less obscured by the chloro- 

 plastid. Stain the preparation with iodin solution and reexamine for the 

 nucleus. Make a drawing of a single cell, about one inch in diameter, to 

 show the structures observed. 



B. Spirogyra 



3. Mount a few filaments of Spirogyra and examine with the low and the 

 high power. Note that the filaments consist of cells which are attached 

 end-to-end. Note the cell walls and the connection between adjacent 

 cells. Note also in each cell the green, spiral chloroplastids with the 

 starch-forming bodies (pyrenoids). 



4. Examine the cell wall carefully and note the thin layer of cytoplasm 

 which lines it. Also the large central vacuole, filled with cell sap, 

 which occupies the greater part of the cell. Focus carefully near the center 

 of the cell and find the nucleus, surrounded by a thin layer of the cyto- 

 plasm and suspended by delicate strands of cytoplasm which run out to 

 the peripheral layer lining the cell wall. Draw a few attached cells. 



C. Elodea 



5. Mount two or three leaves from near the tip of the stem of the water- 

 living plant, Elodea. Examine with the low and high power. Identify 

 the rectangular cells with definite cell wall enclosing the cytoplasm in 

 which numerous green disc-shaped chloroplastids are to be seen. Under 

 favorable conditions a movement of the chloroplastids may be detected. 

 This phenomenon will be studied in a later exercise (B. p. 255). Stain the 

 preparation with a drop of iodin solution and reexamine to find the nucleus. 

 Draw to show the structure as observed. 



1 B. pp. 8-12. 

 251 



