New Zealand Plants and their Story
Bogs and some of their Plants
Bogs and some of their Plants.
According as water varies in regard to the chemicals it holds in solution, so does it offer different stations for plant-life. Certain waters are rich in lime; in others this is wanting to a great extent, and acids are present instead. Therefore the presence of lime-rich or acidrich water sharply separates water-soaked ground into the two classes, swamps and bogs. Of course, transitions exist between these. In addition, the water of a bog is coffee-coloured, and contains a large quantity of organic matter. Those small plants called bacteria, which play such an important rôle in adding the all-important nitrogen-compounds (nitrates) to the soil, are also scarce in bogs.
At a glance, bog-vegetation can be distinguished from that of swamps. The bog - moss (species of Sphagnum) is nearly always present in the former, and forms rounded cushions and hillocks of a whitish colour, on which many of the bog-plants make their home. For-some unexplained reason bogs are physiologically dry, and consequently many of their plants must be protected against drought. It is with these unfortunates, indeed, a case of "water everywhere and not a drop to drink." Many bog-plants, owing to these adaptations, can exist excellently well in dry places. Phyllachne Colensoi, e.g., a beautiful green cushion-plant of most dense habit of growth, thrives equally well in subalpine bogs and at the heads of alpine shingle-slips.
Bogs occur both in the lowlands and mountains. They are common on the narrow peninsula of the far North, and also occupy much ground in Stewart Island, the same brownish wiry-stemmed rush-like plant (Hypolaena lateriflora) being common in both localities. Many identical species occur in both lowland and alpine bogs, and those of Stewart Island at almost sea-level bear a close relationship to those of the Southern Alps.page 111
Sphagnum possesses some characteristics which distinguish it from most other mosses. Its stems at their periphery are provided with thin-walled capillary cells, stiffened by fibrous thickenings, and communicating with one another and with the exterior by round openings. Thus water is rapidly sucked in by the plant and stored up, while by the capillaries formed by the cells it can be conducted downwards to all parts of the plant. Although the surface on which the sphagnum grows may be extremely wet, but little water comes from below, and then only for a very short distance. Thus a sphagnum bog is altogether dependent on the rainfall, and can only exist where this is abundant, an excessive precipitation allowing the plant to occupy even a rock-surface. As the upper portion of a sphagnum cushion grows, its lower part dies, and is converted into peat, great masses of which frequently accumulate. Such peat is used for fuel in many parts of the world, and at Waipahi, in Southland, is cut for that purpose to some extent, though such New Zealand peat is generally formed by many other plants in addition to sphagnum, or this latter may be altogether wanting. The upper surface of a sphagnum bog continues to rise in height, and any plants growing thereon must, like dune vegetation, be able to grow upwards faster than they are buried. The small pine, Dacrydium Bidwillii, common on subalpine bogs, is frequently buried by the too rapid growth of the moss, and may be observed in all stages of burial. On the sphagnum cushions themselves many plants will grow, owing to the absorption of pure water, which cannot live on sour peat itself.
Where a mountain-stream on flattish ground is unable to take away all the water, an excess accumulates, and a bog is formed. In such places shallow pools are frequent, between which are the sphagnum hummocks. Here is the home of another cushion-plant, much resembling Phyllachne, Donatia novae-zealandiæ, and a sedge of similar habit, with leaves arranged like a comb, Oreobolus pectinatus. Other plants occur in plenty—e.g., a small celmisia (C. longifolia var. alpina), another with broader leaves (C. glandulosa), the slender grass Deyeuxia setifolia, certain plants belonging to the rather rare family Restionaceae, Gaimardia ciliata (fig. 53), G. setacea, and G. pallida, all cushion-plants, and looking like mosses. Here, too, will be a dense turf formed by a woody plant, Dacrydium laxifolium, that smallest species in the world of the pine-tree family.page 112
Very characteristic of bogs are the sundews (Drosera), and they deserve, at any rate, a passing word. As shown above, the bog-water lacks available nitrogen. The small, spoonlike leaves of the sundews are provided with glandular hairs, at the end of which a shining drop of fluid may usually be seen. This contains a substance which has the power of acting on animal matter in much the same manner as the gastric juice. Should a small insect alight on a drosera page 113leaf, it becomes entangled in the sticky fluid, and at the same time the hairs bend over and pin the victim fast. Thus does this tiny but bloodthirsty plant procure some of its nitrogenous food. All this family do not dwell in bogs; D. auriculata is a plant of the heath, and climbs over grass-stems, &c. D. pygmaea has a remarkable distribution, having so far been found only at the two extremes of New Zealand—viz., on the Bluff Hill and in the far north of the North Island. It is a tiny plant, no bigger than one's little-finger nail, and so may be easily overlooked.
Species of the genus Gunnera are frequent in lowland bogs. Those near Invercargill contain abundance of G. prorepens. The New Zealand species are quite small—mere pygmies, indeed, in comparison with their huge-leaved Chilian relation (G. chilensis). But, notwith-standing this, both equally afford house-room to a species of Nostoc, a fresh-water alga, somewhat after the manner of Azolla before described. Perhaps the prettiest denizen of the bogs is the pale-blue liliaceous Herpolirion novae-zealandiae, which, when not in flower, may be mistaken for a grass. A companion plant is Oreostylidium subulatum.
The bog umbrella-fern (Gleichenia dicarpa) frequently occupies large areas of boggy ground, its pale-green leaves and brown stems rendering it very conspicuous. A creeping club-moss (Lycopodium ramulosum) is frequent in Stewart Island and on the west of the South Island, and farther north the somewhat similar L. laterale is encountered.
Before leaving the bogs, another flesh-eater must be mentioned, the bladderwort (Utricularia monanthos), a plant with small, showy, purple flowers. The bladderworts are quite without true roots, metamorphosed leaves functioning as such. In some instances the leaves develop in another abnormal way: they construct themselves into small bladders, which are furnished with a lid, which can open only from without inwards. This leads to an arrangement like that of certain mouse-traps, so that a minute aquatic animal may easily enter the bladder, whence it cannot escape, and so is digested in due course by the plant.