308 BOTANY: PRINCIPLES AND PROBLEMS 



714. What evidence is there that bacteria are plants rather than 

 animals? 



715. The minute size of bacteria is thought to be one reason why they 

 are able to maintain such a very high degree of physiological activity. 

 Why? 



716. Why cannot plants well be treated with serums and vaccines, 

 as can animals? 



717. In killing bacteria in liquids by heat, it has been found that 

 several boilings, each followed by cooling to ordinary temperature, are 

 much more effective than one long boiling. Can you suggest a reason 

 for this? 



718. Algae themselves are not harmful in drinking water but their 

 abundance there is often a sign that such water may be dangerous 

 to drink. Why? 



719. Why is it desirable to boil surgical instruments before using 

 them to perform an operation? 



720. Why are coughing and sneezing particularl}' dangerous as 

 means of spreading infection? 



721. Pasteur found that a sample of air taken in Paris contained 

 many bacteria but that one taken in the high Alps was free from these 

 organisms. Explain. 



722. Can you think of any reason, aside from their invigorating 

 climate, which should make a mountainous or arctic region particularly 

 healthful? 



723. Why will food keep longer in "cold storage" than under ordinary 

 conditions? 



724. Why do not dried vegetables and meats decay? 



725. Name at least five different methods which are employed to 

 preserve food and keep it from decaying, and state what makes each 

 method effective. 



726. What group of algae does Rhizopus most resemble in its 

 reproduction? 



727. What forms among the algae do the Mucorales resemble in 

 having plants which look alike but are entirely different sexually? 



728. Some kinds of fungi, notable the truffles, grow only around cer- 

 tain species of forest trees. What explanation for this fact can you 

 suggest? 



