In North America the Indians cover their canoes with Birch bark, and in some snow-covered countries the people use it for tiles with which to roof their houses. Some time ago, when men were digging in the peat-bogs of Lancashire, they found the remains of Birch trees which must have been there for a thousand years. The wood had turned into stone, but the bark was still the same as when it grew on the tree. In April the young leaves (2) cover the tree like a green mist. They are very tiny, the smallest and most fairy-like of all our tree leaves. Each leaf is oval in shape, with a glossy surface, and has a double row of teeth, first a large tooth, then a smaller one, cut unequally all round the edge. The leaf stalk is very slender and wiry, and the twig to which it is attached is very little stouter, so that the leaves dance and rustle in the slightest breath of wind. Sometimes the back of a Birch leaf is covered with fine yellow powder. This powder is really a tiny plant which has made its home on the Birch tree leaf and feeds on it, just as the ivy and mistletoe do on larger trees. In autumn these leaves turn pale yellow, and the moss and heather are strewn with their flakes of gold. There is another stranger makes its home on some of the Birch trees. In spring, before the leaves come, you may often notice curious bunches of twigs that look like crows’ nests high up among the branches. These are caused by a tiny insect which has come to stay on the Birch tree, and, in some way which we do not understand, it makes all the twigs crowd together in that curious manner. “Witches’ Knots” they are called in Scotland. In May the Birch tree is in flower. You know that tree flowers are not so easy to see as meadow flowers: they require to be sought for and looked at carefully if you wish to know about them. The Birch tree has two kinds of flowers, and both are needed if the seed from which new trees may grow is to be made ready. It takes the tree a whole year to prepare one kind of flower. During summer look at the foot of a leaf stalk, where it joins the twig, and you will find two tiny green stamen catkins (4) with all their soft scales tightly closed together. In autumn these little catkins become dark purple, and they hang on the tree all winter. Early in the following spring they change entirely. The scales unclose and the catkins grow longer till they look like a pair of caterpillars loosely shaking in the wind. Behind the scales in these reddy-brown caterpillars you find a mass of flowers, each made up of one tiny sepal, also two slender stamens with small yellow heads. Now look at the other kind of flower, the seed catkin (3). These also are small and green, but they grow singly and are fatter and rounder than the stamen catkins. Their scales never open very wide, but if you look closely you will see behind each scale three little pear-shaped seed-vessels with two slender horns standing up from the top of each.