118 PRACTICAL COURSE IN BOTANY 
17. Is it a mere superstition to drive nails into the stems of plum 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? (124.3 
19. Why isa 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 
Materia. — 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. Red oak shows the medullary 
rays well. Get sticks of green wood, if possible, and have 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? Which 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? es 
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 
