THE PLAXT GROUPS 89 



temperature. Observe the two tubes every fifteen 

 minutes or at such, intervals as you find necessary. 

 Eesults ? How do you explain the differences ob- 

 served in the two tubes ? At the end of an hour 

 test the two tubes for carbon dioxide. Eesult? 

 Write up the above experiment in terms of object, 

 method, results, and conclusions to be drawn con- 

 cerning the nature of fermentation. Indicate method 

 and results by drawings. 



5. Nutrition. Draw a diagram of a yeast plant greatly mag- 

 nified. Indicate the income and outgo of the yeast cell, 

 comparing its nutritive processes with those of Proto- 

 coccus and a specialized green plant. Contrast briefly 

 the nutrition of yeast and that of green plants like 

 Protococcus and Geranium (see Fig. 2 of the text). 



BACTERIA 



CLASS EXPERIMENTS 



1. Expose a sterilized culture dish containing nutrient gelatine, 

 agar-agar, or other suitable substance for bacterial growth 

 in the classroom or laboratory for fifteen or twenty 

 minutes. Expose a second culture dish out of doors or 

 in a quiet room. Cover and observe after the cultures 

 have remained for twenty-four hours in a warm place. 

 a. Are there colonies of bacteria formed on the culture 

 media in both cultures ? Is there any difference in 

 the number and kinds of colonies in the two dishes ? 

 How do you account for any differences observed ? 

 b. Study the colonies with a hand lens or with a low 

 power of a compound microscope. Are there differ- 

 ences in the size, form, or color of the different 

 colonies? Can you account for such differences? 



