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11. Examine the plate cultures. The differently colored and shaped spots 
are colonies of bacteria. Where one colony is separate from the others, uni- 
from in shape, color, and appearance, it is probably a colony or group of 
organisms that has grown from a single cell. 
Select three colonies with the instructor’s approval and mark them 1, 2, 3 
respectively with a pen or with a wax pencil. 
12. Examine them with the 16 m.m. objective. Place the Petri dish, in¬ 
verted, cover and all, on the stage of the microscope. Draw and describe 
them according to the outline in Appendix A. 
(a) What is the difference in appearance of the agar in the dishes, 
(1) as compared to the time when poured into the dishes; 
(2) as compared to each other after one week? 
( b ) Plow may the appearance of the dish labeled “sterile” be 
explained? 
(c) What is the advantage of plate cultures? 
( d ) Who first introduced the plate culture method? 
( e) Why do colonies not form in liquid media? 
(0 Is it always true that each colony forms from one cell? Give 
reasons for your answer. 
