Page:A primer of forestry, with illustrations of the principal forest trees of Western Australia.djvu/44

38 The pictures of many of the principal trees included here will go a long way towards their identification when taken in conjunction with the letterpress. But, for the benefit of those who may desire more intimate knowledge, there are also included drawings of the fruits and flower-buds of certain of the trees.

It should be added that identification by the bark only is not satisfactory. It will be gathered from what has been said previously that only the inner layers of the bark of a grown tree are alive. The outer layers are dead and the cracks in the surface of the bark of old trees are caused by the expanding of wood inside. In very old jarrah, for instance, the bark is deeply indented. In a younger specimen of the same class it is not so deeply indented nor so rough, whereas in saplings and very young trees the bark is quite smooth.

Since it is impossible to identify many of our Eucalypts without a knowledge of their reproductive organs, the following notes contain brief descriptions of the flowers and more particularly of the fruits of our commoner trees. Many of these trees are very similar in general appearance, and even in their bark; but any doubt as to their identity can generally be settled by examining the fruits or "nuts."

The majority of our flowers consist of the following parts: The calyx, which is the outer covering, usually green in colour, and which possesses lobes or sepals which fold over and protect the more delicate portions when in the bud stage. The corolla, which is usually brightly coloured, consisting of petals which serve to attract insects by their bright colour, and also to protect the innermost parts. The corolla lies inside the calyx, and is larger when fully expanded. The stamens, which are arranged inside the corolla, are like small pins. They are arranged in a circle, and consist of two parts; the stalk or filament, which bears on its summit the anther, which is the male portion of the flower. The anthers are covered with pollen. The centre of the flower is occupied by the ovary, which bears a stalk or style on its summit. On the top of the style is the stigma, which is generally shaped like a pin-head, and is slightly sticky. The ovary, style, and stigma collectively form the gynoecium or female portion of the flower.

In the case of Eucalypts, however, the sepals and petals are missing, or rudimentary. In a few species the sepals remain as small teeth, on the calyx, or floral receptacle, and in all the species the petals have become united into the cap or operculum, that little lid which falls off when the bud bursts into bloom. Therefore the operculum performs the protective functions of the sepals of common flowers. The stamens of the Eucalyptus are large and usually coloured, and besides performing their usual functions also serve as petals, insomuch that they are coloured and attractive. The fruit of the Eucalyptus consists of the enlarged calyx, which encloses and is adherent to the capsule, and is hard and woody, assuming various forms. So diversified are these forms that they offer the best means of identifying this large genus.

It is very probable that the Eucalyptus once had large sepals and petals, like those of its near relatives the tea-tree and bottle-brush, and that these parts have been reduced as being unnecessary.