68 



PLANT BIOLOGY 



a girdle will not stop the upward rise of the root water so 

 long as the wood remains alive ; but it will stop the passage 

 of the elaborated or food-stored materials to parts below 

 and thus starve those parts ; and if the girdle does not 

 heal over by the deposit of new bark, the tree will in time 

 starve to death. It will now be seen that the common 

 practice of placing wires or hoops about trees to hold 

 them in position or to prevent branches from falling is 

 irrational, because such wires interpose barriers over which 



the fluids cannot pass ; in 

 time, as the trunk increases 

 in diameter, the wire girdles 

 the tree. It is much better 

 to bolt the parts together by 

 rods extending through the 

 branches (Fig. 85). These 

 bolts should fit very tight in 

 their holes. Why ? 



Wood. — The main stem 

 or trunk, and sometimes 

 the larger branches, are the 

 sources of lumber and tim- 

 ber. Different kinds of wood have value for their special 

 qualities. The business of raising wood, for all purposes, 

 is known as forestry. The forest is to be considered as a 

 crop, and the crop must be harvested, as much as corn or 

 rice is harvested. Man is often able to grow a more pro- 

 ductive forest than nature does. 



Resistance to decay gives value to wood used for shingles 

 {cypress, heart of yellow pine) and for fence posts (mul- 

 berry, cedar, post oak, dot's d'arc, mesquite). 



Hardness and strength are qualities of great value in 

 building. Live oak is used in ships. Red oak, rock maple, 



Fig. 85. — The Wrong Way to 

 brace a Tree. (See Fig. 118). 



