"But there is a difference between them, and as it is not one which you can find out for yourselves, I must tell you what it is. The pines and the firs are resinous trees. Their stems yield the inflammable substances known as turpentine and resin. It iseasy to detect the resinous smell in these woods. The oak stem is not resinous. It yields no liquid of any sort. Hence,you see, we have a second distinction between these two families of trees.
"But we must pass on now to the leaves. Here are some oak leaves. Take them in your hands and examine them. Now describe them.""They are like most of the common leaves," said Willie, "and consist of a blade and a foot-stalk. There are ribs crossing the blade, and a network of veins running all over it.""Quite correct," said Mr. Wilson. "They are the usual leaves of the di-cotyledon; and, moreover, the microscope would show us the breathing pores, studded all over the blade.