THE STEMS KINDS AND FORMS; PRUNING 



57 



FIG. 66. A KNOT HOLE, 

 and the beginning; of a 

 hollow trunk. 



to keep out the germs and fungi. 

 A covering of sheet iron or tin may 

 keep out the rain, but it will not ex- 

 clude the germs of decay ; in fact, 

 it may provide the very moist con- 

 ditions that such germs need for 

 their growth. Deep holes in trees 

 should be treated by having all the 

 decayed parts removed down to the 

 clean wood, the surfaces painted or 

 otherwise sterilized, and the hole 

 filled with wax or cement 

 Stems and roots are living, and 



they should not be wounded or 



mutilated unnecessarily. Horses 



should never be hitched to trees. 



Supervision should be exercised 



over persons who run telephone, 



telegraph, and electric light wires, 



to see that they do not mutilate 



trees. Electric light wires and trol- 

 ley wires, when carelessly strung 



or improperly insulated, may kill 



trees (Fig. 67). 



SUGGESTIONS. Forms of s ferns. 



43. Are the trunks of trees ever per- 

 fectly cylindrical? If not, what may 

 cause the irregularities ? Do trunks often 

 grow more on one side than the other? 



44. Slit a rapidly growing limb, in spring, 

 with a knife blade, and watch the re- 

 sult during the season. 45. Consult the 



woodpile, and observe the variations in FIG. 67. ELM TREE KILLED 



thickness of the annual rings, and espe- BY A DIRECT CURRENT 



dally of the same ring at different places FROM AN ELECTRIC 



in the circumference. Cross-sections of RAILROAD SYSTEM. 



