A most fascinating tree is Sheoke; so also is Buloke. Sombre in appearance and slow of growth, but full of interest to the student. They were commonly called She-oak and Bull-oak respectively, but as these might lead one to think them related to Oak we will fall in with the names adopted by the Victorian authorities. They belong to the genus Casuarina. This genus does not contain many species. It is confined to Australia, the adjoining Pacific, and the East Indies to East Africa. Botanically it is very isolated. It is not immediately related to any other existing group, and it is not possible with our present knowledge to conjecture along what line of descent it has arrived at its present state. Its structure is unique among plants, except that something of a superficial resemblance appears in the Horsetails of the Northern Hemisphere, which are related to ferns, and are a survival of an ancient type which flourished at the period when great beds of coal were laid down. It is quite impossible that Casaurina was in any way a descendant from Horsetail; it is only another instance of a similar form having been produced independently.
Sheoke is a small tree. Its ultimate branchlets are very numerous, drooping, and green; they perform the duties of leaves, for those organs are reduced to little scales, useless for any other purpose than to protect the young growing point. The branchlets arc slender and cylindrical, and are divided into sections by circles of nine to twelve little teeth-like leaves; they are also grooved longitudinally by as many grooves as there are leaves. Though these grooves appear only as faint lines, they sink for some distance into the substance of the branchlet. There are no stomata on the exposed surface; these organs are placed on the walls of the grooves. It can thus be seen, from the absence of effective leaves and the existence of stomata only on very protected areas, that evaporation is reduced to a minimum, a condition not at present necessary in Tasmania, yet Sheoke does very well.
The flowering is very different from any form yet examined. The stamens and pistils are not only produced in different flowers, but, except in unusual cases, are borne on separate trees.
Each staminate flower consists of one stamen, clothed at the base by a few minute bracts, one or two of which are thrown off as the stamen elongates, and are considered to be the representative of a perianth. The staminate flowers are very numerous in the circles of leaves at the ends of branchlets. The pistillate flowers are also numerous in little lateral cones. Each consists of a minute one-celled ovary, a long slender style with two delicate, red, stigmatic branches; each has three small bracts, but no perianth. When in flower the red styles are very noticeable, but not sufficiently so to attract insects. Fertilisation is effected by pollen being accidentally blown on to the stigma by a current of air. Pollen is formed in immense quantity on a Sheoke. There are certainly many million grains produced for every one that reaches an ovule. If you patiently watch a Sheoke with minute staminate flowers you may notice at every slight puff of air a thin cloud of innumerable grains being wafted abroad, and it is seldom that any of them reach their effective destination. The fruit recalls the idea of the cone of a. Pine. It is oblong, about an inch long, and covered with sharp protuberances. The styles have fallen off, but the ovary has become much enlarged, is thick, and ends in a sharp point. When mature each ovary opens in two halves, releasing two winged seeds. The wood is red and beautifully marked with thick radiating rays. It is tough, and valuable for decorative work and furniture. It is an excellent fuel, and it seems a pity it is seldom used for other purposes. The rays are what is known to joiners as silver-grain, and is present in all woods, but in many instances it is too slender to be readily seen. These rays are of use to the tree in affording an easy means of communication between the superficial and deep tissues; they are channels for the transmission of food and air.
Buloke is also a small tree of similar character, but the branchlets are all erect. They are more slender, have only six to eight scale-leaves and grooves, and both staminate and pistillate flowers are present on the same tree. The fruit is smaller, and the ovaries are very short and blunt. Otherwise the details are as in the last.
Dwarf Buloke differs but slightly. It is a small shrub-with some pubescence on the branchlets and more succulent cones. It is common in heathy country, and not very distinct from the last.
Scoevola Aemula, R Br. [See p. 94
Casuarinas have much the appearance of Cypress and Pine, and they show some details common to these. The structure of their organs and tissues is, however, very different, and there is probably no true relationship.
Beech is unfortunately known as Myrtle, which gives quite an erroneous idea of its relationship. It belongs to an order rare in Australia, but which provides the greatest part of the forest of the Northern Hemisphere. Beech, Oak, Walnut, Willow, Poplar, and many other genera of trees are its relatives.
Our common Beech is a medium-sized tree, with evergreen foliage. The leaves are dark-green, thick, about half on inch long, roughly triangular, and marked on the margin with few coarse serrations. The flowers are obscure, and not often observed. Stamens and pistils, as in all the order, are in separate flowers. The staminate flowers are formed close in the axils of the leaves towards the ends of the branches. There are generally a few together; each has a small six-lobed cup-like perianth, and about eight pendulous stamens. The pistillate flowers are also small, axillary, and near the ends of the branches. Three minute flowers are formed within many bracts, the four inner of which enlarge and enclose the fruits, which are small, flat, or three-winged membraneous nuts.
A parasitic fungus is often found growing upon the branches, which it causes to grow into knobs. It is about the size of a pigeon's egg, is apricot-coloured, and marked all over by pits. It is edible, but tasteless.
In Fuegia there are Beeches closely allied to ours, and, strange to say, they also have parasites very like but distinct from ours.
We have a second Beech which is confined to the mountains of the western half of Tasmania. It has generally the habit of a very spreading wiry bush. It sheds its leaves in winter, which is an interesting fact, as it is the only native that does so. Some of the Beeches of Fuegia also do this. Those of the Northern Hemisphere always have this habit. The leaves are of a rather pale blue-green, and are deeply sulcate on the surface. The flowers and fruit do not differ in any material way from those of our common Beech.
Beeches very similar to ours are found in New Zealand and Fuegia. No members of the genus are found in the tropics or warmer temperate zones. This and a similar distribution of many other plants lends some weight to the idea of recent land connections along the intervening space.
Beech, like Sheoke, is fertilised by the accidental blowing of pollen on to the stigma. In order to ensure this a relatively enormous amount of pollen has to be formed This is not economical; it appears, when compared with many simple cases of insect fertilisation, to be a prodigal waste. Yet in many cases of the latter, as, for instance, in Silver Wattle, the same prodigality is exhibited. All the earlier types of flowering plants are wind-fertilised. Adaptation to gain the assistance of honey-loving animals seems more recent, though not necessarily very modern. We must always remember that the records preserved in rocks, and translated by students of fossils, are few, and their study is quite a young science; wherefore we must yet wait patiently, and not be in a hurry to come to conclusions about the little information already dug out. Tn the past geologists have been so anxious to fix incomplete specimens with names, that much error has been committed. A great many forms claimed as ferns that exist in the coal measures are now known, or suspected, to be more nearly related to seed plants. It is very difficult to resist the temptation to describe new forms and explain matters according to what appears to us to be probable; but when information is meagre, the chance of being wrong is much greater than the chance of being right. Hasty conclusions are responsible for many opinions and theories that are not easily unlearnt.
On the other hand too great caution will only retard advance. The great strides in knowledge which the human mind has made in recent times is in no form more marked than in the reform or abandonment of the theories upon which we had hitherto based our conclusions. Yet, if we had not held tentative but erroneous theories, we should not have advanced to our present condition. If we did not hold opinions till there was undeniable proof of their exactness, we should not hold any opinions at all.
The fossil remains of plants are being subjected to a steady revision. It is not only the carboniferous flora that is being reorganised, but the more recent species founded on leaf-impressions have to be considered. We have credited old Tasmania with possessing a copious flora of Oaks, Willows, Elms, and other trees on the evidence of leaf-impressions; it is very possible we shall have to modify this view.