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 A L G M 269 4.—Rhodophycejs, or Floride^e. —The members of this group persistent basal cell that the branches of unlimited growth arise. are characterized by the possession of a red colouring-matter, Upon them also the reproductive organs arise in this family. It phycoerythrin, in addition to chlorophyll. There is, however, a is not surprising, therefore, that they have been regarded as the considerable amount of difference in the shades of red which mark rudiments of leaves. In Iridcea the thallus is an entire lamina ; different species. The brightest belongs to those species which in Callophyllis a lobed lamina ; in Delesseria it is provided with grow near low-water mark, or under the shade of larger Algae at midrib and veins, simulating the appearance of a leaf of the higher levels; species which grow near high-water mark are higher plants ; in Constantinea the axis remains cylindrical, and usually of so dark a hue that they are easily mistaken for brown the lateral branches assume the form of leaves. In the compact seaweeds. Rhodophyceoe are mostly marine, but not exclusively tlialli a secondary development often takes place by the growth so. Thorea, Lemanea, Tuomeya, Stenocladia, Batrachospermum, of rhizoid-like internal filaments. They present a hypha-like Balbiania, are genera belonging entirely to fresh water ; and appearance, running longitudinally for considerable distances. Bangia, Chantransia, Caloglossa, Bostrychia, and Delesseria It is not difficult in such compact species to distinguish between contain each one or more fresh-water species. Most of the larger superficial cells, whose chief function is assimilation, subjacent species of marine Rhodophycece, are attached by means of a disc cells charged with reserve material, and a core of tissue engaged to rocks, stones, or shells. Many are epiphytic on other Algse, in the convection of elaborated material from part to part. more especially the larger Phceophycece and Rhodophycece. As An interesting feature of the minute anatomy of Eufloridece, in the case of epiphytic brown seaweeds, the rhizoids of the as the Red Algae, exclusive of the Bangiacece, have been epiphyte often penetrate the substance of the supporting Alga. termed, is the existence of the so-called Floridean pit. When Some Red Algae find a home in the gelatinous substance of Flustra, a cell divides it is found that there remains in the middle Alc.yonidium, and other polyzoa, only emerging for the forma- of the new wall a single large circular pit, which persists tion of the reproductive organs. Some are perforating Algae and throughout the life of the cells, becoming more and more conburrow into the substance of molluscan shells, in company with spicuous with the progress of the thickening of the wall. These certain Green and Blue-green Algae. Some species belonging to j>its serve to indicate the genetic relationship of adjacent cells, the families Squamariacece and Corallinacece grow attached when they form a compact pseudo-parenchyma, notwithstanding through their whole length and breadth, and are often encrusted the fact that somewhat smaller secondary pits appear later with lime. The forms which grow away from the substratum between any contiguous cells. Protoplasmic continuity has been vary greatly in external configuration. In point of size the observed in the delicate membrane closing the pit. largest cannot rival the larger Brown Algae, while the majority Vegetative multiplication occurs only sparingly in Rhodophycece.. require the aid of the microscope for their investigation. Melobesia callithamnioides gives rise to multicellular propagula ; No unicellular Rhodophycece are known, although a flagellate Grijjithsia corallina is said to give rise to new individuals, by organism, Rhodomonas, has recently been described as possessed detaching portions of the thallus from the base of which new of the same red colouring-matter. If the sub-group, Bangiaceoe, attachment organs have already arisen. The spores of Monobe excluded, they may be said to consist exclusively of spora are by some regarded as unicellular propagula. Reprobranched filaments. Growth in these cases takes place by means duction is both asexual and sexual. It is noteworthy that of an apical cell, from which successive segments are cut off by although all the members of the group are aquatic no zoospores means of a transverse wall. The segment so cut off does not are produced, a negative character common to them and the Blueusually divide again by means of a transverse wall, nor indeed green Algae. As a rule the asexual cells and the male and female by a longitudinal wall which passes through the organic axis sexual cells arise upon different plants, so that the species may of the cell. New cells may be cut off laterally, which become be said to be tricecious. Numerous exceptions, however, occur. the apical cells of branches. When the new cells grow no Thus in Lemaneaccoe asexual spores are unknown ; in Batrachofurther, but constitute a palisading round the central cell spermum, Bonnernaisonia, and Polysiphonia byssoidcs both kinds covering its whole length, the condition is reached which of sexual cells appear on the same plant; and in some cases characterizes the species of Polysiphonia, the “siphons” of the asexual cells may occur in conjunction with either the male which may be regarded as one-celled branches. To the law that or female sexual cells. The asexual cells are termed tetraspores no subsequent transverse division takes place in segments cut on account of the usual occurrence of four in each sporangium. off from the apical cell, there seem to be two exceptions: first, What may be termed monospores, bispores, and octospores, the calcareous genus Corallina, in the pliable joints of which however, are not unknown. The sporangia may be terminal or intercalated division occurs ; and, second, the Nitophyllece, in intercalated. When they are confined to special branches, such which, moreover, median longitudinal division of axial cells is branches are spoken of as stichidia. The tetraspores may arise said to occur. Like the Fungi, therefore, the Red Algse consist by the simultaneous division of the contents of a sporangium, for the most part of branched filaments, even where the thallus when they are arranged tetrahedrally, or they may arise by appears massive to the eye, and, as in the case of Fungi, this fact two successive divisions, in which case the arrangement may is not inconsistent with a great variety of external morphology. be zonate when the spores are in a row, or cruciate when the In the great majority the thallus is obviously filamentous, as in second divisions are at right angles to the first, or tetrahedral some species of Callithamnion. In other species of that genus when the second divisions are at right angles to the first and an apparent cortication arises by the downward growth of also to one another. Tetraspores a.e at first naked, but soon rhizoids, which are retained within the gelatinous wall of the acquire a cell-wall and germinate without a period of rest. The axial cells. In Batrachospermum the whole system of branches male sexual cells are produced singly in the terminal cells of are retained within a diffluent gelatinous substance derived from branches. They are spoken of as spermatia. Great numbers of the outer layers of the cell-walls. In other cases the mucilage is antheridia 'are usually crowded together, when the part is denser and the branches more closely compacted (Hehninthora). distinguishable by the absence of the usual red colour. In In such cases as Lemanea, the terminal cells of the lateral Polysiphonia they cover the joints of the so-called leaves; in branches form a superficial layer which has all the appearance Chondria they arise on flattened discs ; in the more massive forms of a parenchyma when viewed from the surface. In Champia they arise in patches on the ordinary surface; in a few cases and allied genera, the cylindrical axis is due not to the deriva- {Gracilaria, Corallina, Galaxaura) they line the walls of tives of one axial filament, but of several, the growth of which conceptacle-like depressions. The female sexual cell is repreis co-ordinated to form a septated tube. The branching of the sented by the contents of a cell which is terminal on ordinary thallus, which meets the eye in all these cases, isdueto the unlimited or specialized branches. This is the carpogonium ; it consists growth of a few branches. When such a lateral branch over- of a ventral portion which contains a nucleus, but in which no tops the main axis whose growth has become limited, as in Ploca- oosphere is differentiated, and an elongated tubular portion known mium and Dasya, a sympodium is formed. For the most part the as the trichogyne, into which the cytoplasm extends. Fertilization branching is monopodial. Besides the differentiation into holdfast is effected by the passive convection of a spermatium from the anand shoot, and into branches of limited and branches of unlimited theridium to the trichogyne, to which it adheres, and to which it growth, there appear superficial structures of the nature of hairs. passes over its nucleus through an open communication set up at These are for the most part long, thin-walled, unicellular, and the point of contact. The nucleus then passes down the trichocolourless, and arise from the outer cells of the pseudo-cortex, gyne and fuses with that of the egg. This fusion has been or from the terminal cells of branches when the filaments are observed by Wille in Nemalion multijidim, and by Schmidle in free. Among Rhodomelacece, hair-like structures of a higher Batrachospermum. It is singular that in the last-named species order are known. These arise from the axial cell, and are multi- two nuclei occur regularly in the spermatium. The ventral porcellular and branched. They soon fall off, and it is from the tion of the carpogonium may be imbedded deep in the thallus in the massive species ; the trichogyne, however, always reaches the 1 These include :— surface. The first effect of fertilization is the occlusion of the 1. Bangiaccce—4 families, 9 genera, 58 species. trichogyne from the fertilized carpogonium. The subsequent 2. Nemalionince—4 families, 33 genera, 343 species. course of development is characteristic of the Florideoe. The 3. Gigartinineoe—3 families, 54 genera, 409 species. carpogonium germinates forthwith, drawing its nourishment 4. Rhodymenince—4 families, 92 genera, 602 species. almost wholly from the parent plant. The ultimate product (De Toni’s Sylloge Algarum.) in all cases is a number of carpospores, but before this stage 1