The Myrtles form by far the most conspicuous feature of Tasmanian woodlands. Eucalypts, Bottlebrushes, and Teatrees are the commonest genera, while the pretty little Baeckias and Native Broom assist in adding interest to our heaths. These, with a few more, are the Tasmanian representatives of the family. We call our Beech by the name Myrtle; this is wrong, and should be suppressed Beech is quite as easy, and has the advantage of being correct.
The name is given to the family because the European Myrtle is a typical member of it. Like the Roses, we have here many forms of fruit. In Myrtle and some Australian forms it is fleshy, like a berry, but our plants have mostly dry capsules, though Native Broom and our rare Thrypto-mene have little one-seeded nuts. Besides the structure of the flower, there is one common feature in all our forms - little glands of oil are formed in the leaves. These can be seen by holding a leaf up to the light, when they appear as pellucid dots, or crushing them in the hand, when the odour of the oil can be readily perceived. This formation of oil dots is not confined here; we find it also in the Rue family, to which belong Boronia, Native Fuchsia, and Stinkwood, but it is uncommon elsewhere. It is worthy of notice that very often amongst plants when an unusual feature appears, as, for instance, this formation of oil drops, or the possession of some poisonous principle, it is common to the whole group to which the plant belongs, though in varying degree. The leaves of all the members of this large family are of simple outline; that is, they are never broken up into lobes or leaflets.
This family is well defined by general features, but it differs from the Roses in its flowers. The carpels are blended together, so that the pistil appears as one body, and in the floral tube is united much more consistently to the pistil. This appears a small matter, but it is another step in advance towards a higher type, where the tube completely envelopes the carpels so as to bring the ovary below the flower.
A Teatree may be taken as a type. It has pretty little flowers, like miniature single roses. They are placed singly in the axils, or at the ends of short branches, and have very short stalks. The floral tube is well developed, and closely blended with the pistil for some distance, in many cases even to the top of the ovary. This union is so close that tube and ovarian wall appear like one structure. Above there is always a free portion to the tube. From the end of the tube arise five small triangular sepals, and closely above and alternating with them five round, spreading, white or pink petals. The stamens arise close above the petals, and are numerous. As the condition of the stamens is largely made use of to separate the closely-allied genera, we must pay some attention to them. They are all free from one another, arranged in a single row, and are shorter than the petals. The filaments are slender, and attached by a point to the back of the small oblong anthers. There are usually five carpels, but in one Teatree there are ten. The ovarian portions of these carpels are arranged in a circle, and where their walls touch they are so blended that there appears only a simple division between the cavities and at least in their lower portions they are intimately united with the floral tube. From the centre above and from a slight depression arises a slender, simple, erect style, terminated by a little head, which is the stigma. At the inner angle of each ovarian cavity there is a little cushion of tissue, upon which are developed numerous minute ovules. Any cushion or place where ovules grow is called the placenta.
In developing into fruit the condition does not much change. It only becomes somewhat larger and harder, the sepals in most cases remaining on the top of the rim. The top of the fruit may be flat or convex, sometimes in the same species, and it splits in a radiate manner along the top of each ovary to allow the seeds to escape. These seeds are small and slender, and the genus of Teatrees has been named from this fact. The name is Leptospermum, which means slender-seeded. The Teatrees are not all well marked; some forms run very much into one another. The Woolly Teatree is the commonest. It has a flat blunt leaves, and the green portions of the flower are more or less covered with delicate hairs. It prefers damp situations. Manuka or Prickly Teatree is also common, but it prefers open places and hillsides. The leaves have a sharp termination, and the fruit is very convex, a large part of it protruding above the tube. There is one thing worth noticing in it. that flowers that bear well-developed stamens often have stunted and barren ovaries. This tendency to separate the functions of stamens and pistil is much more pronounced in some other flowers, as we shall see when we refer to this later on. A third rather common form is the Slender Teatree, found in damp sandy heaths. The leaves are regularly oval. The fruit is small tor the genus and quite flat-topped; also, it becomes rather fleshy at maturity.
We have five different shrubs, commonly known as Bottlebrushes. They owe their name to the peculiar arrangement of their flowers. These are formed many at a time. They are without stalks, and arranged close together, so as to form a dense mass of flowers closely massed towards the ends of the branches. The sepals and petals are small, but the stamens are long and stand straight out, so that when in bloom the whole has very much the appearance of a bottle cleaner. These five plants belong to two genera, four in one and one in the other Having no very distinct popular names, it will be necessary to use their botanical ones. The first is Melaleuca; the second, Callistemon. Melaleuca means black-white, in allusion to the shades of bark seen on a shrub by an early observer. Callistemon means beautiful stamens, and as in many Australian species these are a brilliant red. we can feel more sympathy with this name than we can with the other. The two genera are very close, and run into one another. They differ in general appearance, but the principal contrast is that in Melaleuca the stamens are arranged in five definite bundles, with their filaments more or less united below. In Callistemon they are variously arranged, according to the species, but never so clearly collected into five bundles. In our Melaleucas the union of the stamens is very short, so that the distinction is less pronounced than it is in most mainland forms. In both genera the anther cells are parallel, and attached to the filament in the middle of its back. There are other Australian genera that differ mainly in another form of anther. In all our Bottlebrushes the base of the flower is buried in the bark, and the fruit persists during life so that the old capsules may be seen still on the bark, marking each year's flowering. The floral tube is united to the ovary, and extends beyond it; the five small sepals are persistent; the petals are small, and much exceeded by the numerous stamens. The other details of the flower do not differ materially from the condition found in Teatree.
Purple Bottlebrush. (Melaleuca squamea, Lab.) [See p. 42
Yellow Bottlebrush is a rigid shrub found in wet places. The leaves are short, broad, and arranged in opposite pairs, so that each pair is placed at right angles to those above and below it. The flowers are always yellow. Purple Bottlebrush is a shrub of damp heathy places. The flowers may be either purplish or yellow. The leaves are less broad, and alternately arranged. Dwarf Bottlebrush is a pretty little shrub of heathy country. The small flowers are purplish, the leaves only about one line long, and arranged in opposite pairs. Swamp Bottlebrush also known as Swamp Teatree, only occurs in the north. It grows into a small tree, has yellow flowers, and small linear alternate leaves. Our only Callistemon is a shrub of the hills. It bears copious yellow flowers, and flat leaves fully an inch long.
We have only two or three Baeckias, and they have no popular names. May not the botanical one be popularised ? Baeckia is just as easy and pretty as any other is likely to be, and it certainly will not lead to confusion. The common one is a pretty little wiry shrub, that raises itself amongst undergrowth in heaths. The leaves are narrow, and about a quarter of an inch long. The flowers are on rather long stalks, but are shaped otherwise very much as they are in Teatree, only the stamens do not exceed ten, and there are only one or two seeds in each cell of the capsule. The petals are pinkish-white.
Native Broom is unfortunately named, as it is not a relation to, nor is it a bit like, the true Broom. It is a small shrub of heathy land. The flower is not like, the Myrtles we have examined, and at once distinguish it. The floral tube is long and slender: it is just like a stalk, but it is intimately blended with a contained ovary, which bears but one ovule. Above the ovary it is continued in a slender stalk-like condition for some distance, when it suddenly produces five diverging sepals. These are connected together at the base by a thin membrane, but the points are elongated into spreading slender bristles. The petals are five, and stamens many, but neither are conspicuous.
The Myrtles are chiefly plants of warm, sunny places. Though a few of them can withstand the intense cold of a high altitude, none of them extend to a high altitude, They are well adapted to dry conditions. The leaf surface is small; its skin is thick, and covered by an impervious cuticle often coated with wax. This condition is eminently suited to reduce evaporation.
Plants respond to their surroundings. Individual plants may be profoundly influenced, so may the race, yet there appears to be no connection between this individual change and the race change. In other words, the character of a plant may, by peculiar conditions of feeding or exposure, be much modified, but it has no power of transmitting this modification to its offspring. The seed may be poor or well filled out, according as the plant has been ill or well fed, and a weak or robust plant may result, but no other condition is transmitted. Thus many plants which, if grown in ordinary soil have thin leaves, will, if the soil contains much salt, become thick and fleshy, but will immediately again produce thin-leaved young if their seed is planted on normal soil. A fern growing on our mountain tops is copiously hairy, but if it is brought down to a low elevation the new leaves gradually lose that condition. The seed-producing parts of a plant are the oldest and best fixed of its organs, and they appear to do their work along fixed lines without transmitting any personally acquired character. This is at variance with popular ideas, but is the result of overwhelming evidence in both animal and vegetable kingdom. The persistent change in habit is due to other and racial causes, and will be dealt with in a subsequent chapter. Therefore, we must look on the adaptation of Myrtles to Australian conditions to be other than the response of individuals.