190 



HISTORY OF THE VEGETABLE KINGDOM. 



where they are pei'petually floating in an agi 

 tated medium; others dwell in the hollows of 

 rock, or in the marine gulfs, where the water is 

 generally calm. The lapse of a few days puts a 

 period to the existence of some kinds, while the 

 tempests of successive winters fail to destroy 

 others. The general aspect is apt to change in 

 several individuals, so that were it not for more 

 stable characters derivable from their fructifica- 

 tion and texture, they might be mistaken for 

 new species. A number of the more delicate 

 marine plants are quickly destroyed by a re- 

 moval from their native place of growth; but 

 the greater proportion being coriaceous, and in- 

 soluble in salt water, live for a leng-th of time 

 in diiFei-ent situations; and it is not uncommon 

 to find upon our own shores the algae of the 

 most distant regions which have traversed the 

 ocean, and yet remain unchanged in their general 

 appearance. From these circumstances it bears 

 a necessary inference, that it is not all the algs 

 that are found in any country which may be 

 said to belong to that country. 



But there are few kinds of sea weed that pre- 

 fer any particular spot, or show a predilection 

 of one substance over another whereon to fix. 

 Deriving no nutriment from the roots or points 

 of attachment, they need nothing farther than 

 a temporary support. Thus they cling indis- 

 criminately to any solid marine body, equally 

 to granitic and calcareous rocks, to floating or 

 sunken pieces of wood, to the bones of terres- 

 trial or marine animals, to shells or polypi. 

 Notwithstanding that very highly respectable 

 naturalists have averred that the growth of these 

 plants proceeds with most vigour on such and 

 such substances, on some or other peculiar rock 

 in the vicinity of rivers, or in the open sea, it 

 has been fully ascertained, says Dr Hooker, by 

 a great number of observations, that marine 

 weeds do grow with equal vigour, though planted 

 upon rocks or substances of very different na- 

 tures; and that, if we except some few uhce, 

 which aff^ect brackish water, those which vege- 

 tate in situations where fresh water mingles with 

 the salt, are generally bleached, produce little or 

 no fructification, have a thin and weak textm-e, 

 and contain but little soda. The qualities re- 

 quisite for their different uses are only found 

 united in such sea weeds as grow in pure salt 

 water, where tliey have found a spot which is 

 sufficiently tenaceous to fix them in that zone 

 of habitation which they prefer. Some kinds 

 certainly prefer sand or mud; but then their 

 roots become elongated and strike deep, till they 

 meet with some stone or shell, or other body, 

 which may serve them as a point of attachment, 

 and offer the requisite degree of resistance. 



If the nature of the bottom appears indifferent 

 in a great measure, to marine plants, it is not so 

 with the level which they select in the ocean. 



or with the distance of their birth place from 

 the surface. Every species of maritime vege- 

 tables appears to make choice to as great an ex- 

 tent as the terrestrial kinds of certain zones or 

 regions of different depths in the sea; places 

 where the superincumbent weight of water, and 

 the relative proportions of light and heat, are 

 adapted to its peculiar organs. Those individuals 

 which are found towards the centre of their 

 proper zone, contain all the elements requisite 

 for their perfect development, and generally show 

 an active state of vegetation: they are vigorous; 

 they fructify at the season suitable to their de- 

 gree of immersion; while those that grow at the 

 extreme limit, or out of the bounds of this same 

 zone, prove languishing, fructify imperfectly, 

 are always covered with marine animals, which 

 destroy them, and live but a short time in com- 

 parison with their better situated congeners. 

 The seeds which escape from these plants would 

 appear by their various specific weights to gain 

 an equilibrium equivalent to the column of 

 water which they displace; or, in other words, 

 to float in that peculiar zone which the future 

 algae would prefer to inhabit. Those which be- 

 come developed either above or below it, ai-e 

 inevitably driven from their spot of nature or 

 of election, by the agitation in the waves at the 

 vicinity of the coasts. 



Lower down than 100 feet from the surface 

 of the sea, taking a medium between the high 

 and the low tides, it is rare to find living sea 

 weeds in the gulf of Gascony, and even these 

 are attached to portions of rock severed from 

 more elevated rocks, and before long they inevi- 

 tably perish. It may be observed that the deeper 

 we explore the waters of the ocean, the fewer 

 will the number of plants appear; and the more 

 numerous the polypi, or plant-like animals. 

 Thus, below the depth of forty feet very few 

 ulvas are found; beyond sixty feet no living 

 cermium, and after having descended to the depth 

 of 100 feet, not a fucus is to be seen, and vege- 

 table objects entirely disappear. 



The laminaricB, among which are the giants 

 of the marine flora, exhibit, in a general view, 

 a tolerably decided geographical distribution. 

 This family predominates from the 40th° to the 

 65th° of latitude; while another family, the 

 macrocystes, seem to extend from the equator to 

 about the 45th'' of south latitude. 



The laminaria digitata is the well known 

 tangle so abundant on the British coasts. The 

 stem is from one to six feet in length, and from 

 a half to two inches in diameter; solid, very 

 tough, and in old plants woody, expanding at 

 the top into a flat frond, one to five feet or more 

 in length, and about nine to twelve inches in 

 width. In England it is known by the name 

 of sea girdles. In Scotland, where the tender 

 stalks of the j'oung fronds are eaten, it is called 



