74 ESSENTIALS OF BOTANY 



mentioned (Sect. 63), and count the rings of wood above and below 

 eacli ring of scars. 



How do the numbers correspond? What does this indicate? 



Count the rings of wood on the out-ofi ends of large billets of 

 some of the following woods : locust, chestnut, sycamore, oak, hickory. 



Do the successive rings of the same tree agree in thickness ? 



Why ? or why not ? 



Does the thickness of the rings appear uniform all the way round 

 the stick of wood? If not, the reason in the case of an upright 

 stem (trunk) is perhaps that there was a greater spread of leaves on 

 the side where the rings are thickest or because there was unequal 

 pressure caused by bending before the wind. 



Do the rings of any one kind of tree agree in thickness with those 

 of all the other kinds? What does this show? 



In all the woods examined look for : 



(a) Contrasts in color between the heartwood and the sapwood.^ 



(i) The narrow lines running, in very young stems, pretty straight 

 from pith to bark, in older wood extending only a little of the way 

 from center to bark, the medullary rays shown in Fig. 42.^ 



(c) The wedge-shaped masses of wood between these. 



(rf) The pores which are so grouped as to mark the divisions 

 between successive rings. These pores indicate the cross-sections of 

 vessels or ducts. Note the distribution of the vessels in the rings to 

 which they belong ; compare this with Fig. 45 and decide at what 

 season of the year the largest ducts are mainly produced. Make a 

 careful drawing of the end-section of one billet of wood, natural 

 size. 



Cut off a grapevine several years old and notice the great size of 

 the vessels. Examine the smoothly planed surface of a billet of red 

 oak that has been split through the middle of the tree, and note the 

 large shining plates formed by the medullary rays. 



Look at another stick that has been planed away from the out- 

 side until a good-sized fiat surface is shown, and see how the medul- 

 lary rays are here represented only by their edges. 



1 This is admirably shown in red cedar, black walnut, barberry, black 

 locust, and osage orange. 



2 These and many other important things are admirably shown in the thin 

 wood-sectious furnished for $5 per set of 24 by R. B. Hough, Lowville, N.Y. 



