100 



FOUNDATIONS OF BOTANY 



a solid steel or iron rod of the same size would be too 

 stiff for this use. 



111. The Dicotyledonous Stem, thickened by Secondary Growth. 

 Cut off, as smoothly as possible, a small branch of hickory and one of 

 white oak above and below each of the rings of scars already mentioned 



(Sect. 77), and count the 

 P rings of wood above and 

 below each ring of scars. 



How do the numbers 

 correspond? What does 

 Phi this indicate ? 



Count the rings of 

 wood on the cut-off ends 

 of large billets of some 

 of the following woods; 

 locust, chestnut, syca- 

 more, 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 rea- 

 son in the case of an up- 

 right stem (trunk) is per- 

 haps that there was a greater spread of leaves on the side where the 

 rings are thickest l 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. 2 



1 See Sect. 118. 



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

 locust and osage orange. 



JR 



FIG. 71. Cross-Section of a Three- Year-Old 



Linden Twig. (M\ich magnified.) 

 P, epidermis and corky layer of the bark ; Phi, bast ; 

 C, cambium layer ; Jit, annual rings of wood. 



