INTERRELATIONS OF PLANTS AND ANIMALS 127 



2. What would happen if organic matter did not decay ? 



3. May these bacteria be useful or harmful to man? 



FlG - ^- Useful bacteria which change dead mat- 



* i -r-r. , 



ter into food for grass, wheat, and corn. Highly 

 magnified. 



2. SOME OTHER USEFUL BACTERIA 



Observations. 1. Set aside some cream in a moderately 

 warm place for a day or so. Results ? Odor and taste ? 



2. Squeeze some 

 juice from apples. 

 Set it aside as 

 above. Results? 



3. Set aside some 

 fresh grape juice as 

 above. Results? 



4. Bruise an ap- 

 ple or banana. Set 

 it aside in a moder- 

 fltP warm nlsPA for 



duv5 \\ dl 111 IJlciOc i-UL 



several days. Re- 

 suits ? 



5. Explain how linen fibers are prepared. 



6. Which sort of cheese is considered the better, that 

 freshly made or that aged ? Explain. 



7. What causes nodules to form on the roots of such plants 

 as clover, alfalfa, bean, etc.? (See page 82.) 



Conclusions. 1. What is the benefit of ripening or souring 

 cream ? What has probably caused it to do so ? 



2. What is the result of the action of bacteria on the alcohol 

 of fruit juices ? Note. The alcohol was formed by the action 

 of yeast from the air or on the fruit, fermenting the sweet 

 juices, resulting in cider, wine, etc. The alcohol is then 

 attacked by bacteria, which change it into an acid (acetic acid) 



3. W T hat is meant by decay? Note. An example of decay 

 of starch might be represented as follows : 



Decay = Starch 4- oxygen = carbon dioxide -f- water 

 C,H 10 5 + 6 2 = 6 C0 2 + 5 H 2 



