The Parents' Review

A Monthly Magazine of Home-Training and Culture

Water Plants

The northern lakes are naturally the home of many water plants. The list of their denizens, if drawn up, would be a long one, for there is great variety of elevation from the larger lakes at low level to the little rock-circled tarns under the summits of the mountains; the waterfalls, too, have their own flora, little Filmy Ferns that luxuriate in scattered spray, and mosses that grow thrivingly even in tossing water. A few hours poling about in a boat one summer day in 1893, among reeds and water-weeds revealed matters rather different from the usual end of July conditions. The lakes had been very low all the spring months, and the plants of the margin had suffered. Of the Greater Spearwort, Ranunculus Lingua, I saw only two plants instead of the usual twenty or thirty. The Reed-mace, Typha latifolia, the candle-wicks of the country folk, is usually in evidence; it might not have flowered much, but it had already all been cut down, one brown spike dropped told the tale. Summer visitors are great sinners from a botanical point of view; they want to carry away with them some of our treasures; only want of knowledge on their part and lack of conspicuousness in some of our rarer plants save them to us. I tried to count the flowers that make up one of these thick brown spikes. I cut off a quarter of an inch and divided that into quarters, but the minute florets baffled my patience; instead of petals they have hair-like bristles and adhere together thereby. The only part of the flower which is seen, giving the mass its rich brown colour, is the withered stigma. These are pressed tightly together in great numbers, over-topping the floral hairs and entirely concealing them. By the time the spike has grown thick and changed from green to brown, the male flowers above have withered and vanished. The more slender plant, Typha angustifolia, is smaller in all its parts, and the male spike is separated from the female flowers below by as much as an inch or two of bare stem; on this plant there are often two sets of female flowers, one below the other, their masses equally long. The male flowers are monadelphous, some with three anthers, others with two, but many also with only one anther. The slender jointed hairs of these staminate flowers are few, often one to each, those of the pistils are much more numerous.

The white Water-Lilies fringed all the shallower bays; the yellow ones were already over, only large green pear-shaped fruits full of yellow seeds, replaced petals and stamens in the persistent calyx caps. The leaf and flower stems are traversed by air cavities, and in these spaces grow pretty stellate hairs; in the larger intercellular spaces, on the under side of the leaves, the same hairs are to be seen. I have been wondering if there are any properties or characters that are common to water plants as a whole, and if these same long air-passages may not be considered as characteristic of plants living in water, giving them the necessary lightness of structure to push up to the surface of the water and float there. Water plants, too, seem destitute of hairs, outwardly at least, or do they all grow them internally like the Water-Lilies-not that I am at all sure that these are true hairs-could they be many-armed cells, part of the general cell structure, before the formation of the air-passage? The wall structure of air-spaces often shows interesting forms; they are generally covered by the remains of the cells at whose expense the cavity has been formed, or the whole space is loosely filled with the remnants of cells. The hollow begins by those cells which are ceasing to grow becoming separated from one another by the growth beyond them; the in-growing cells get broken, lose their protoplasm, dry up and coalesce to flaky masses attached to the wall of the cavity. In Bulrush (Scirpus lacustris) the dark green round glossy stems are full of white tissue, enclosing air-spaces, but the texture and form is very different, so much stiffer and less succulent; here are hair-like strands of broken up cells, but they are manifestly dead remnants, not living cells as the stellate hairs of Yellow Water-Lily (Nuphar lutea).

[Heinrich Anton] De Bary describes the structure of the Bulrush stem thus:--"The contents of the halms become differentiated into prismatic bands of stellate lacunar tissue, separated by plates of dense parenchyma, which appear in cross section, as a net with angular meshes. The stellate cells follow the growth of the latter, their arms elongating greatly; finally they become broken up, and only dried remains are left in the prismatic space."

The Bulrushes are in perfection in July; the anthers are then gone, and at least half the flowers in every head have set into fruit; all the floral organs, except anthers and stigmas, which are necessarily exposed for wind fertilisation, are so well wrapped up in the awned and scarious brown glumes, that they must be pulled to pieces to be understood; the perianth here is reduced to six hair-like bristles, edged with down-turning points or serrations; they are pretty objects under a good lens, and the glumes, too, are lovely in colouring, streaks of reds and browns running irregularly into translucent margins. I never see here any of the leaves that are mentioned in the books as sometimes produced by this tall plant.

In Lobelia Dorimanna the middle layer of the leaf is soon destroyed to form air-passages, making one cavity on each side of a persistent centre plate: the flower stem is also hollow. This plant is one of the specialties of the lakes. I know it only in shallow water, two to three feet deep, in gravelly places. Looking over the side of the boat, its upstanding leaves appear as a dense green mat: a whole plant, roots and leaves, will generally come up with the flower stem. In 1893 the flowers came early in June; I searched in vain for a flower in mid-July, and found only a few fruiting stems, and they were quite submerged, the water had risen with the late rains, and the lake surfaces were at a higher level. When the capsule is submerged, the seeds have still a means of exit; the substance of the capsule at its lower part dissolves away, and the seeds fall out between the strands that built up the structure and that are then left white and stringy-looking. In the cross section of the capsule, the little spots round the edge represent the drops of latex which formed there on the cutting of the section. The tubes containing the latex differ here from those of Spurge (Eupharbia) in being articulated; they are very fine and delicate, running and branching throughout the plant, but are without any recognisable minute structure. The seeds are at first of a pretty crimson colour, which finally becomes brown.

The large water grasses were found to be in different phases of life. The Reed Grass (Phalaris arundinacea) was past its flowering time, with empty glumes; while the Great Reed (Arundo Phragmites) had not yet come in full flower, its purple panicles still neither a foot long nor decorated with their silky hairs. There were three Pondweeds in flower and fruit, Potamogeton perfoliatus, Potamogeton obtusifolius, and the tiny Potamogeton pusillus, common enough lake plants. Myriophyllum spicatum was, as usual, in great masses. The Pondweeds differ from most petaloid monocotyledons by having four stames and four carpels, but the perianth leaves are considered in their case to be out-growths of the stamens, or scales from the connective.

A day's boating on Windermere, early in August, gave me a water plant that I had long sought in vain; it grows at the bottom of the lakes, mostly below arm's reach from a boat: it is more specially a water plant than any other that I have known, excepting only the various species of Chara, for it is perfectly independent of the surface, and sends nothing up there, neither stem, leaves nor flower. It is an apparently stemless plant, the very short one that it has being entirely hidden by wide-based, clasping leaves, 10 to 20 of them from two to six inches long, stiff, awl-shaped and spreading in all directions. I found some half-dozen of these Quillworts, all perfect plants, floating at the verge of a shallow bay. A lake storm had, but I know not quite how, uprooted them, and they had drifted to the edge. At first I did not quite know what I had found, never having seen them before. They were not very unlike Lobelia Dortmanna without the flowering stem. The resemblance is greater in the living than in the dried plant; the difference was easily determined by cutting a leaf in two and finding that it contained four, not two, longitudinal air cavities. There is not a hint of flower or bud to be seen, but this is not a flowering plant at all; it is a cryptogam, a vascular cryptogam, classed with ferns and horse-tails and club-mosses. Its reproductive organs are hidden, wrapped up in the bases of the leaves, and it is only when you have broken one of them off that you see what is there. Isoetes seems a very solitary genus, with no near relatives, there being nothing else at all like unto it with our flora; it is classed next to Selaginellae, a water-loving plant, too, but of very different habits. The two genera have this in common, that they each bear two kinds of spores, large female macrospores and small male microspores; Quillwort has no other leaves than spore-bearing ones, while Selaginella only sends up in the middle of summer a branch or two of fertile leaves.

The awl-shaped leaves of Isoetes lacustris are winged in the lower part, also they are in section a round, flattened somewhat on the upper side. Like the leaves of many other water plants they are traversed by wide air passages, four in this case, and a weak vascular bundle occupies their axis. These air spaces arise from separation of tissue, consequent on unequal surface growth; some transverse zones however, follow the growth and so remain connected at certain places, forming septa or diaphragms which break the continuity of the passages at rather regular intervals. The septa consist of many-armed cells connected by the ends of the arms, forming a plate with wide lacunae; these diaphragms are white and shining, and are distinctly visible in the lower part of the unbroken leaf, as paler bands or rings in its green surface. The wider part of the leaf, the sheath which partially embraces the stem, rises from a broad insertion, it is convex behind, concave in front, and here is the large depression, the fovea, in which the spore-case lies. The edge of the depression rises into a thin membrane outgrowth, surrounding and almost enclosing the sporangium, which has, therefore, all the appearance of being embedded in the leaf. Above the spore-case is a curious little ligule, a sort of upturning tongue, what it is exactly I don't know. It soon becomes brown, and I have not been able to see it as well as it is portrayed in Goebel's drawing, but it gives the name to two groups of plants, Selaginellae and Isoeteae, and they are classed together as Ligulatae. Such are the leaves of Isoetes lacustris, and a rosette of them is formed every year; the outer leaves of this fertile rosette produce only macrosporangia, containing a large number of macrospores; the inner leaves bear only microsporangia. Both kinds of sporangia are imperfectly divided into compartments by strands of tissue stretching across from front to back of the spore-case; the spore-cases do not open, the spores are only set free by decay of their walls.

The plant so far described is the asexual generation only, as are the ferns; the sexual one consists of two individuals, each extremely minute, resulting from the development of the macrospores and the microspores respectively. The microspore lies dormant during the winter, and then goes through the changes which result in the production of four mother cells of spermatozoids. These spermatozoids are long and slender spirals terminating at both ends in pencils of cilia; the spiral body is produced by the splitting up of the thickened periphery of the nucleus of the mother cell, and it lies coiled round a central vacuole which often remains hanging to the extremity, after the spermatozoid has escaped from the mother cell, and is carried about with it. This course of development occupies about three weeks, from germination of the microspore to the perfect spermatozoids which move freely in the water by means of their cilia, but not for longer than five minutes. The macrospores produce the female plant, the prothallium, entirely within themselves. A few weeks after, they are set free from their decaying envelope, the coat of the spore becomes thicker and assumes a granular appearance, while the inside has become divided up into cell tissue, the spherical prothallium, whose swelling causes the splitting of the spore coat in the form of a three-rayed aperture, the spore coat (endosporium) then softens and peels off, leaving the prothallium bearing at its apex one or more apchegonia ready for the fertilizing spermatozoids; two canal cells in the neck of the archegonium are converted into mucilage and ejected in order to admit the spermatozoids to the oosphere. We see in this plant that the sexual generation, the prothallium, has almost disappeared, occupying only the interior of the macrospore whose coat bursts merely to give the spermatozoids access to the archegonium. It has almost lost the character of an independent plant, and may be said to form a link between the cryptogams and the phanerogams or seed plants. Their macrosporangium is the ovule with sporogonous tissue reduced to a few cells and enclosed in one or two envelopes from which the seed coat is afterwards formed; these envelopes differ from those of the vascular cryptogams (indusia) in being part of the macrosporangium itself, and not luxuriant outgrowths of the leaves which bear it, as in ferns and Isoetes. The microspores of the Seed Plants too, the pollen grains, are said to produce a rudimentary prothallium, if only of one cell. That the microspores of Quillwort rest during the winter in a unicellular condition before beginning their subdivision into spermatozoids, necessitates that the macrospores of this year's plants are fertilized by the male elements produced by last year's plants.

In Selaginella the sporangia are formed from the surface of the stem above the leaf, though they seem to occupy the axil of the leaf and to be seated on its base below the ligule; they grow in dense spikes in the upper parts of special branches. Like Isoetes, the macrospores are below and the microspores on the higher part of the fertile branch. Selaginella is such a very different looking plant that one would never think of classing it with Isoetes; it much more resembles in general structure the Lycopodiceae among which it used to be placed, but which produce only one kind of spore.

The short and simple stem of Isoetes is remarkable for its want of growth in length, no internode being formed; the upper part occupied by the leaves is the shape of a shallow funnel, lower in the centre, where is the apex, than round the circumference; the constant growth in thickness marks off this stem from all other cryptogams, it grows from a layer of meristem surrounding the central vascular group which is always producing new layers on the outside; this increase takes place in several directions on the cross section and causes the projecting masses like bulbs or corms, which gradually turn brown and die off on the outside; between these masses are furrows giving rise on the under side to numerous bifurcating roots. This tuber-like stem has no pith, its axile vasculae bundle is made up of united ends of the bundles of the leaves, one from each leaf. It is only in very few plants that no branching takes place, that there is no formation of growing points of secondary shoots. The stem of Quillwort grows for years and yet it is always short, because growth is taking place more energetically transversely to the axis than parallel to it; it produces leaves and roots but never any side shoots. This stem, like that of all true water plants, is devoid of wood, the leaves surrounded by water can take up for themselves all that they require and need no active current coming up from the root.

S. Armitt.

Proofread by LNL, July 2020