Humboldt and Bonpland describe,* under the name of Fucus vitifolius, (as already mentioned,) a species of a fine grass green colour, brought up, at l'Alegranza, from the great depth of 192 feet, at which depth it had vegetated. The light at that depth could only have been equal to half the light of an ordinary candle ; yet, according to Hum boldt's experiments, common gat den-cresscs, exposed (lur ing vegetation to the light of two Argand's lamps, acquire only a slight tint of green. That distinguished philosopher therefore concludes, that it is only under the influence of the solar rays, however weak, that the carburct of hydrogen is formed in the organs of plants, the presence of which makes the parenchyma appear of a lighter or darker green, according as the carbon preponderates in the mixture.
The colour of all the soft and annual fuci depends on a very fugaciouS extractive. Those that are horny in texture retain their colour with more force. Several of them be come of a greenish hue when boilecl ; and every one who has seen dulse fried, must have remarked the change to green produced by the application of heat. The ultimate tendency to a green hue observable in several species, may probably be ascribed to the more complete developement of the alkali contained in the plant.
To the botanist it may be useful to know, that when there is reason to suspect that the appearance of the plant is changed by exposure to the air or rains, the original co lour may often be detected by holding up the specimen against a strong light. For example, F. sinuosus, which is frequent on the stems of F. digitatus, and has fronds re sembling in shape the leaves of Alnus incana, is, when fresh, of a rosy red colour; in decaying on the shore, this changes first to violet, and then to tile red: but on holding the specimen against the light, the original rosy hue may be detected. Wahlenberg notices concerning F. plumosus, that when repeatedly washed in fresh water, it becomes green ; that, in dilute muriatic acid, it preserves its colour, and when removed from it becomes green, as if an alkali had been poured on it.
Another species, F. ericoides, (Turn. t. 191), possesses ‘he more extraordinary property of reflecting bright glau cous tints when seen under water in a growing state. It is naturally of a yellowish green colour, but under water ap pears as if in a state of vivid phosphorescence. On with drawing it from the sea, the brightness vanishes. The phe nomenon has not been thoroughly examined. This focus
grows on the shores of Devonshire and Cornwall ; but Mr Stackhouse, who spent his days in those districts, and had many opportunities of observing the appearance, only says that the colour resides in, or is occasioned by a slimy mu cus which covers the frond. When dried, the plant comes of a reddish brown colour.
Concerning F. ligulatus, a species which occurs, though not plentifully, on out' shores, and is excellently figured by Lightfoot in his Flora, (t. 29,) Professor Mertens mentions a curious fact: in the sea it is of an olive green colour; but as soon as it is brought in contact with the air, it becomes of a deep orange, or rather the colour of decayed leaves. The only specimens we have seen, which were taken from the rubbish of a fishing-boat at Newhaven in the Frith of Forth, were of a pale dull green ; but to this colour, Mer tens observes, the orange tint soon declines.
It has been remai lied of some of the smaller and more delicate foci, that the same species seems to vary in ap pearance, size, and especially colour, according to the na ture of the substance to which it happens to be attached, whether a stone of shell, or the stem of a larger sea-weed. But this observation is by no means of universal applica tion. Variations are more generally occasioned by the cli mate in which the plant grows ; the depth or water ; the exposed or sheltered nature of the situation; or the proxi mity to the mouth of a river or body of flesh water.
General Distributiott of Fuci.
A few remarks on the general distribution of the foci may here be made. Some may be considered as properly pelagic, as F. pyrifcrus, (Turn. t. 110), the gigantcus of Foster, or the badreux of' the Falkland Islands. This sends out numerous fronds, and the upper and under fronds are frequently found soldered as it were together, at certain spots of the edges. This species occurs v., abundantly in the South American seas as to resemble islands, and it is one of the chief of the gigantic fuel al luded to by circumnavigators. Linnaeus merely says, that it is the longest and largest of the fuci. Solander mea sured some of the apices, and found them to be from ten to twelve feet ; but he gives no guess as to the length of the entire plant, which is said to extend from 500 to 1000, or even 1500 feet. F. notatorum of Labillardiere, is another of the great pelagic fuci, of such ample dimensions, that particular parts of it furnish various household implevuents to the natives of New Holland.