PRACTICAL WORK 75 



(2) Draw an active specimen in successive stages of motion 

 to show the change of shape depending on the protrusion and 

 withdrawal of pseudopodia. See if you can observe an amoeba 

 in process of ingesting another organism as food. 



(3) Kill the amoeba by running a drop of iodine or acetic methyl 

 green under the coverslip and note that the nucleus is stained more 

 deeply than the cytoplasm. 



(4) Examine a demonstration specimen of amoeba which has 

 been fixed, stained and permanently mounted, showing the 

 deeply stained nucleus. 



B. PROTOCOCCUS AS A TYPE OF SIMPLE PLANT. 



(1) Scrape off a little of the green crust from the bark of a 

 tree into a drop of water and cover with a coverslip. Examine 

 with the low power and note the numerous green specks and 

 clumps in the field of the microscope. Put on the high power 

 and distinguish cell wall, chloroplast, and colourless cytoplasm. 

 The chloroplast generally contains a bright granule, the pyrenoid. 

 More than one chloroplast may exist in the cell. The nucleus 

 is usually difficult or impossible to distinguish. It lies in the 

 colourless cytoplasm, often in the concavity of the curved 

 chloroplast. 



(2) Examine stages in the division of the cells (only found 

 when the Protococcus is kept damp) (a) when the new cell 

 wall is not yet formed but the chloroplasts of the daughter cells 

 are distinct, and (b) after the cross wall is formed but the two 

 daughter cells are still clearly derived by division of the parent 

 cell. Add a drop of very dilute iodine solution and observe the 

 effect. 



