118 PRACTICAL COURSE IN BOTANY 



17. Is it a mere superstition to drive nails into the stems of plmn and 

 peach trees to make them bear larger or more abundant fruit ? (126, 127.) 



18. Why is a living corn stalk heavier than a dry one ? (124.) 



19. Why is a stalk of sugar cane heavier than one of corn ? Suggestion : 

 Which is the heavier, pure water, or water holding solids in solution? 



V. WOOD STRUCTURE IN ITS RELATION TO INDUSTRIAL USES 



Material. — Select from the billets of wood cut for the fire, sticks of 

 various kinds ; hickory, ash, oak, chestnut, maple, walnut, cherry, pine, 

 cedar, tulip tree, all make good specimens. Rod oak shows the medullary 

 rays well. Get sticks of green wood, if possible, and liave them planed 

 smooth at the ends. Collect also, where they can be obtained, waste bits 

 of dressed lumber from a carpenter or joiner. If nothing better is avail- 

 able, any pieces of unpainted woodwork about the schoolroom will furnish 

 subjects for study. 



130. Detailed structure of a woody stem. ^ Select a 

 good-sized billet of hard wood, and count the rings of annual 

 growth. How old was the tree or the bough from which it 

 was taken ? Was its growth uniform from year to year ? 

 How do you know? Are the rings broader, as a general 

 thing, toward the center or the circumference? How do 

 you account for this ? Is each separate ring of uniform 

 thickness all the way round? Mention some of the cir- 

 cumstances that might cause a tree to grow less on one side 

 than on the other. Are the rings of the same thickness in 

 all kinds of wood ? WTiich are the more rapid growers, those 

 with broad or with narrow rings? Do you notice any dif- 

 ference in the texture of the wood in rapid and in slow grow- 

 ing trees? Which makes the better timber as a general 

 thing, and why ? 



131. Heartwood and sapwood. — Notice that in some 

 of your older specimens (cedar, black walnut, barberry, 

 black locust, chestnut, oak, Osage orange, show the differ- 

 ence distinctly) the central part is different in color and text- 

 ure from the rest. This is because the sap gradually abandons 

 the center (116, 123) to feed the outer layers, where growth 

 in dicotyls takes place; hence, the outer part of the stem 



