Coralline algae

“ The rapidity with which walls, piles and pontoons—stone, wood and iron—become covered with marine plants is well known, while the discovery of some effective means of preventing the fouling of the bottoms of ships by the growth of algae would be hailed as a boon by shipowners. While rocks and boulders are the favoured situation for the growth of marine algae, those which readily disintegrate, like the coarser sandstones, are naturally less favoured than the hard and resistant. A large number of algae again live as epiphytes or endophytes. ”

“ In such rocks land-plants must necessarily be rare. There are, however, limestones which wholly or in part owe their formation to masses of calcareous algae, which grew in the form of submarine banks or on coral reefs. Occasionally the remains of these algae are clearly preserved, but frequently all signs of plant structure have been completely obliterated. Again, there occur limestone rocks formed by chemical means, and in a manner similar to that in which beds of travertine are now being accumulated. ”

“ Around the coast-line of land areas, and on the floor of shallow seas algae exhibit a remarkable wealth of form and luxuriance of growth. As regards habit and structure, there is every gradation from algae in which the whole individual consists of a thin-walled unseptate vesicle, to those in which the thallus attains a length unsurpassed by any other plant, and of which the anatomical features clearly express a well-marked physiological division of labour such as occurs in the highest plants. ”

“ Several genera live as endophytes in the tissues of other algae. The recent species of this section of algae are characteristic of temperate and tropical seas. One subdivision of the red algae, the Corallinaceae, is extremely important from a geological point of view and must be dealt with in some detail. ”

“ There is no golden rule, and we must admit the difficulty of separating real fossil algae from markings made by animal or mechanical agency. The presence of a carbonaceous film is occasionally a help, but its occurrence is no sure test of plant origin, nor is its absence a fatal objection to an organic origin. While being fully alive to the small value of external resemblance, and to the numerous agents which have been shown to be capable of producing appearances indistinguishable from plant impressions, we must not go too far in a purely negative direction. ”

“ Excepting where the thallus is impregnated with silica, as in Diatomaceae, or carbonate of lime, as in Corallinaceae, Characeae and some Siphonales, it is perhaps not surprising that algae should not have been extensively preserved in the fossil form. Considering, however, that it is generally believed that Bryophyta and vascular plants are descended from an algal ancestry, it is natural to suppose that, prior to the luxuriant vegetable growths of the Carboniferous period, there must have existed an age of algae. ”

“ There is considerable difficulty in removing mounted specimens of algae from paper, and therefore a small portion preserved on mica should accompany each specimen, enclosed for safety in a small envelope fastened at one corner of the sheet of paper. Filamentous diatoms may be mounted like ordinary sea-weeds, and, as well as all parasitic algae, should whenever possible be allowed to remain attached to a portion of the alga on which they grow, some species being almost always found parasitical on particular plants. ”

“ The canals which these algae produce in calcareous shells and other hard substances are of the same type as those previously described in fossil corals, fish-scales and bones. In dealing with living perforating Thallophytes the colour and other cell-contents often enable us to distinguish between algae and fungi, but in fossil specimens such tests cannot be applied. The fossil tubular borings may or may not show traces of the transverse septa and reproductive cells ”

“ Each class of flowerless or cryptogamic plants requires special treatment for the herbarium.
Marine algae are usually mounted on tough smooth white cartridge paper in the following manner. Growing specimens of good colour and in fruit are if possible selected, and cleansed as much as practicable from adhering foreign particles, either in the sea or a rocky pool. Some species rapidly change colour, and cause the decay of any others with which they come in contact. ”

“ Evidently the oxygen thrown off by the alga is precisely what the plant needs, and the carbonic acid and nitrogenous waste eliminated by the animal is most useful to the alga. Moreover, the algae gain the advantage of ready locomotion with their host, and the animal can go further into unfavorable media when stocked with algae ready to build up starches and sugary matters from carbonic acid and water. ”

“ Before discussing our knowledge, or rather lack of knowledge, of fossil algae at greater length, it will be well to briefly consider the manner of occurrence and botanical nature of existing forms. In the sea and in fresh water, as well as in damp places and even in situations subject to periods of drought, algae occur in abundance in all parts of the world. ”

“ This is the case in the remarkable symbiosis between algæ of the family Nostocaceæ and the floating, moss-like water-fern Azolla. This plant, in external appearance almost like duckweed, has on the under surface of its leaves a minute opening, leading into a relatively roomy hair-lined cavity, and in this cavity there is always, enclosed in jelly, a bluish green unicellular alga, Anabæna. The cavity is present in every leaf, and the alga is present in every cavity, making its way in from a deposit of alga-cells which is found on the incurved tip of every young shoot. ”

“ These zoophytes increase by gemmation or budding; some throw up germs from the disk, as in Astreadæ; others laterally, as in Caryophillidæ; and some spirally along the stem, as in Madreporidæ; examples of these modes of reproduction are often found in fossil corals. The increase of coral-rocks is produced by the continual formation of new masses, by the successive generations which spring up as it were from the bodies of their parents; layer upon layer, and tier upon tier, of Helianthoid polypidoms, are found to compose many of the coralline limestones of the palæozoic formations. ”

“ The bases of the larger seaweeds growing on rocks between tide-marks are nearly always thickly covered with encrustations of Flustrella hispida or of species of Alcyonidium, in places where they are kept moist by being covered with a sufficiently thick layer of other algae. Rocks which are protected from the sun may be coated with calcareous Cheilostomes; and these are also found, in company with branching Polyzoa of various kinds, on the bases of the Laminaria thrown up by gales or exposed at spring tides. ”

“ Most algae, particularly Phaeophyceae and Rhodophyceae, spend the whole of the life-cycle immersed in water. In the case of the freshwater algae, however, belonging to the Chlorophyceae and Cyanophyceae, although they required to be immersed during the vegetative period, the reproductive cells are often capable of resisting a considerable degree of desiccation, and in this condition are dispersed through great distances by various agencies. ”

“ With all its fantastic beauty a coral reef is cruel. Nearer the shore the stony blocks are overspread by masses of that singular skeleton-less coral, known as alcyonaria—partaking of the nature of rubber and of leather—an ugly, repulsive, tyrannous growth, over-running and killing other and more delicate corals, as undesirable pests crowd out useful and becoming vegetation. It occurs in varying colours and forms—sickly green and grey, bronze and yellow, brown and pink. ”

“ Avoid the common and coarser kinds (fuci) which cover the surface of the rocks; for they give out under water a slime which will foul your tank: but choose the more delicate species which fringe the edges of every pool at low-water mark; the pink coralline, the dark purple ragged dulse (Rhodymenia) , the Carrageen moss (Chondrus) , and above all, the commonest of all, the delicate green Ulva, which you will see growing everywhere in wrinkled fan-shaped sheets, as thin as the finest silver-paper. The smallest bits of stone are sufficient, provided the sea-weeds have hold of them ”

“ Decaisne had pointed out in 1842 that certain marine organisms previously regarded as animals should be transferred to the plant kingdom. Such seaweeds as Halimeda, Udotea, Penicillus and others were thus assigned to their correct position. Many fossil algae belonging to this group continued to be dealt with as Foraminifera until Munier-Chalmas demonstrated their true affinities. In Gümbel’s monograph on the so-called Nullipores found in limestone rocks, published in 1871 [315] , several examples of siphoneous algae are included among the fossil Protozoa. ”

“ The builder coral, glimmering in its softer parts with delicate hues and tints, throws up its stony barrier through a thousand miles of length and a third as much in breadth, fringing the continents with bays and sounds and atoll islands like fairy rings of the sea. Animate flowers—sea-nettles, sea anemones, plumularia, campanularia, hydropores, confervae, oscillatoria, bryozoa—people the great waters. Sea-urchins, star-fish, sea-eggs, combative gymnoti, polypes, struggle and thrive with ever-renewing change of color; gelatinous worms that shine like stars cling to every weed ”

“ Amid these shrubs of precious coral, I observed other polyps no less unusual: melita coral, rainbow coral with jointed outgrowths, then a few tufts of genus Corallina, some green and others red, actually a type of seaweed encrusted with limestone salts, which, after long disputes, naturalists have finally placed in the vegetable kingdom. But as one intellectual has remarked, "Here, perhaps, is the actual point where life rises humbly out of slumbering stone, but without breaking away from its crude starting point." ”

“ Meanwhile it is extending outward on its own talus, and at the same time débris and sand are cast continually shoreward, and, with the help of smaller coralline growths, fill up the interstices of the shore coral until a solid bank is formed, which, by further aid from the waves of the sea, and from the land and its vegetation, is raised above high water and in time becomes dry land. ”

“ The deposition, moreover, of sediment, checks the growth of coral-reefs, so that these two agencies cannot act together with full effect in filling it up. We know so little of the habits of the many different species of corals, which form the lagoon-reefs, that we have no more reasons for supposing that their whole surface would grow up as quickly as the coral did in the schooner-channel, than for supposing that the whole surface of a peat-moss would increase as quickly as parts are known to do in holes, where the peat has been cut away. ”

“ For early June cuttings, forty parts per million appears to be adequate. The softer the cuttings, the weaker should be the solution.
Algae:
In both the cold frame and the cold room the growth of algae is a problem. The sand medium becomes crusted, with subsequent interference with aeration. The algae sometimes creeps up the stems of cuttings, coats the leaves, and covers terminal buds. Starting each season with completely clean sand and equipment will not prevent the appearance of algae over a long season of continuous operation. ”

“ At length these granules fill the cells, are black under the microscope, and the algae emit an offensive odor. In the Campagna marshes are formed in winter, which in spring develop algae abundantly. In summer the water disappears, and the algae then putrefy, the ground afterward growing phanerogamous plants. Toward the fall of the year the algae in the parts still covered with water also die, and the slime at the bottom of the marshes contains quantities of the dark granules. ”

“ The corals, also, on the margin of Keeling Island occurred in zones; thus the Porites and Millepora complanata grow to a large size only where they are washed by a heavy sea, and are killed by a short exposure to the air; whereas, three species of Nullipora also live amidst the breakers, but are able to survive uncovered for a part of each tide; at greater depths, a strong Madrepora and Millepora alcicornis are the commonest kinds, the former appearing to be confined to this part, beneath the zone of massive corals, minute encrusting corallines and other organic bodies live. ”

“ The coral grows until it reaches the surface. It is known to flourish best in the foaming breakers. These, although confronted and in the main resisted by the wondrous tubes and cells, are able here and there in violent storms to break off the weaker or overhanging portions of the coral and dash them in fragments upon the top of the reef. Often the waves are loaded with battering-rams in the shape of immense quantities of drift-timber. These bring with them innumerable seeds and hard nuts able to retain their vitality while traversing leagues of ocean. ”

“ It has been shown in the chapter on Keeling atoll that there are some species of large fish, and the whole tribe of Holothuriæ which prey on the tenderer parts of the corals. On the other hand, the polypifers in their turn must prey on some other organic beings; the decrease of which from any cause would cause a proportionate destruction of the living coral. The relations, therefore, which determine the formation of reefs on any shore, by the vigorous growth of the efficient kinds of coral, must be very complex, and with our imperfect knowledge quite inexplicable. ”