PROBLEM 87 111 



The method of science can, however, be used and all reasonable care and accu- 

 racy be given in the performance of any experiments which follow. 



The informational content is certainly of the widest possible importance. An 

 entire course could well be devoted to the numerous experimental questions which 

 present themselves. It is unwise, however, to give more than a month to six 

 weeks' time to the chapter because of the need for balance in the course. 



Materials for the study of bacteria (nutrient agar or gelatine) may be obtained 

 from any good chemist, from manufacturing chemists, and from the local board of 

 health. Directions for making culture media follow in this chapter, but the 

 work need not be given up because of lack of proper apparatus or laboratory facil- 

 ities. 



Problem 87: To determine the relation of fungi to the de- 

 struction of certain trees. 



NOTE. — Suggestions for field trip to work out loss of trees by the attack of 

 shelf fungus and chestnut canker. A field trip to a park or grove near home may 

 show the great destruction of timber by these means. 



a. Shelf Fungus 



Observations. — Count the number of perfect trees in a given 

 area. Compare it with the number of trees attacked by the 

 shelf fungus. Does the fungus appear to be transmitted from 

 one tree to another near at hand? In how many instances can 

 you discover the point where the fungus first attacked the tree? 

 Do healthy trees seem to be attacked? 



Conclusion. — ■ Under what conditions will shelf fungus attack 

 a tree ? 



b. Chestnut Canker 



Note. — • Chestnut canker is spread by tiny reproductive bodies called spores. 

 These, if they obtain a foothold on a sound tree, soon grow to form plants which 

 feed upon the tree, ultimately causing its death. 



Observations. — In a given area are all the chestnut trees dead 

 or dying? How might tiny spores get from one tree to another? 

 What appears to be the first sign of the disease in a tree ? Pull off 

 the bark of an infected tree and note the silvery threads running 

 in every direction. These form the body of the canker called the 

 mycelium, which reaches out after food. What part of the tree 

 would it be likely to attack and why ? 



NOTE. — A plant or animal which lives at the expense of another living plant or 

 animal is called a parasite. 



Is the canker a parasite ? 



