If, however, still further proof of the rapid growth were wanted, the experience of the following season afforded ample evidence. In autumn 1814, a course of large hewn freestone was completed, and the operations were again suspended till the following summer. It was as late as the beginning of July 1815, before the weather permitted boats to approach the rock at low water ; when, on the new course of the beacon, a crop of Focus esculentus was found, the fronds of which measured on an average six feet long, and were, as before, furnished with pinnx. This must of necessity have been the growth of not more than eight months from the time of the very minute seeds having at tached themselves to the hewn stone.
The opinion of Lamouroux, therefore, that during win ter the vegetation of sea plants is suspended, like that of land plants, is proved to be erroneous.
It may here be mentioned, that Dr Walker states,* on the authority of the kelp-makers, that " sea-weeds do not grow so much in seven years upon freestone as they do in two years on whinstone." The facts above detailed spew that this remark is not universally applicable, although it may be true of the loose masses of stone on the shores, which, if soft, must be liable to be worn by the striking of smaller boulder stones.
It is not improbable, that the growth of the large pela gic fuci may even be much more rapid than that now de scribed. The Focus giganteus of the Pacific Ocean attains several hundred feet in length : Forster mentions speci mens even 800 feet long. In the bays of this country, F. filum frequently reaches 30 or 40 feet, and in some places, as Scalpa Flow in Orkney, this is considered as the growth of the summer and autumn months, from May to October.
General Structure, &c. of Fuel.
From the characters of the orders in Lamouronx's ar rangement, some notion of the general structure of the dif ferent tribes of marine plants must already have been ac quired. In treating farther of the same subject, brevity shall therefore be studied.
In general it may be observed, that some species are co riaceous, often branched and shrub-like ; some are mem branaceous, and traversed by a longitudinal nerve or mid rib ; others are filiform, generally not jointed they produce receptacles, tubercles, or capsules ; and most of them are furnished with air-vesicles.
Decandolle considers marine plants as composed entirely of cellular tissue ; attributing the difference of structure observable in the stems, the midribs or nerves, and the fronds, to modifications in the form of this cellular tissue. Mirbel is of the same opinion. It is certain that all the parts of sea plants are much more nearly of uniform tex ture than in land plants in general ; most of them seeming to be capable of changing into others ; the peduncle be coming a branch, the air-vesicle a frond, and so on. La
mouroux, however, has remarked, that the stem of Focus digitatus is formed of four distinct parts, analogous in si tuation, relative size, and even organization, to the epider mis, bark, wood and pith of dicotyledonous plants. It per haps requires some aid from the imagination to enable the observer to see all this. But it is certain that a section of the stem of Fucus digitatus toms a curious microscopic object, and that it is distinctly perceived to be composed of longitudinal parallel jointed colourless fibres, disposed in concentric circles, and constituting altogether a pretty solid mass. Larnotnoux has likewise discovered, or imagined he has discovered, in certain sea-weeds belonging to differ ent tribes, most of the characters which distinguish the brilliant corollas of plimnogamous plants, the stems and leaves of trees, and the herbaceous structure in general.
That marine alga; are not furnished with continuous ves sels of the same nature as those of land plants is obvious, from the well known remark, that, if one portion of a sea plant be plunged in water, and the other left exposed to the air, only the immersed portion remains in vigour ; no fluid seems to rise speedily enough through the frond to nourish or refresh the other part of the plant. The result of micro scopic observation, and attempts at injection, support the same view. On the other hand, the fructification of some families, as the Fucacex and Floridex of Lamouroux, is observed to be placed almost always on the stems or branches, near to the masses of fibres, or at their extremi ties. In the Dictyodem of the same writer, the more regu lar and visible the structure of the reticulations, or cellular tissue, appears, the situation of the fructification is found to be more uniform ; and the less regular and distinct, the fructification is more scattered. The production of cap sules regularly at the extremities of branches or fronds, which is observed in many species, proves the existence of some kind of vessels, and the elaboration of particular fluids. Upon the whole, therefore, as something analogous to circulation is indispensable, the masses of fibres, or cel lular tissue with lengthened cells, may be considered as calculated to perform the functions of longitudinal vessels. Horizontal vessels are distinctly seen in some species, par ticularly F. vesiculosus and nodosus.