The bark of the oak is very rugged, with ridges and furrows running almost vertically. Fig. 113.—The Oak; leaves, flowers and fruit. A, flowering branch (× ¼); B, a male flower (magnified); C, stamens (magnified); D, a female flower (magnified); E, acorns; F, cup of acorn; G, H, seed. The young shoots which are formed when the buds expand in spring are short, and the leaves are set closely together. As a result, the oak’s foliage is characteristically dense and thick. The leaves are very distinctive; their general shape is oval, and the margin is deeply and irregularly lobed (Fig. 113). If in early spring we go out in the woods and fix on an old oak tree (the oak hardly ever flowers before it is 50 years old), we shall probably see the flowers on some of the young twigs. The female flowers—one to five on each flower-stalk—are near the end of the twig, while the male flowers arise lower down. The female flowers are destitute of stamens, each consisting practically of a single pistil, partially enclosed in two envelopes, the lower of which ultimately becomes the familiar “cup” of the acorn. The stigma has three spreading [Pg 145] lobes for receiving pollen. The male stalks or catkins, hang down from the lower part of the twig, and every stalk bears about a dozen flowers. The male flowers have each from 5 to 12 stamens, but they have no pistil. The stamens produce pollen in the usual way, and when they burst, the wind blows the loose pollen from the stamens and scatters it in the air. Some of the pollen dust is almost certain to be wafted to the stigmas of the female flowers, and the pollen grains put out tubes, and in due course fertilise the ovules. Fig. 114.—The Beech. [Pg 146] Most of our forest trees resemble the oak in being pollinated by the aid of the wind. It is evident that for the process to be successful the trees must flower early in the spring, before the foliage has become so thick as to be in the way of the pollen and prevent it from reaching the stigmas of the female flowers. It is also important that the pollen may be easily detached, and it is for this purpose that the male flowers of the oak and similar trees hang down in the familiar catkin fashion. Fig. 115.—The Beech. 1, flowering branch (× ⅔); 2, a male flower (× 4); 3, a female flower cut through longitudinally (× 2); 4, cross section of ovary; 5, cup and fruits (× ⅔); 6, fruit. After fertilisation the female flower changes into an acorn (Fig. 113, E), a nut enclosed in a cup. The nut contains a single large seed, which on germination grows up into a new oak. Galls of various kinds are to be found on most oaks. These are excrescences caused by certain insects having laid their eggs in the [Pg 147] soft tissues beneath the surface. More than fifty species of insects obtain their food from the oak. Some of these will be referred to in a later chapter.