TRANSPIRATION. 



17 



FIG. 16. Wood of the Eastern Sycamore or Button-ball tree. 



FIG. 17. Cross section through a Black Oak. Milford, Pa. The silver grain, 

 the rings of annual growth, and the dark heart wood and lighter sap wood are 

 A'isible, and the line between the rough corky outer bark and the thinner and 

 lighter-colored inner bark may be seen. 



