UNATTACHED ROOTS.

29

years. Some plants, which in their native warm countries are perennial, as the mignonette, and nasturtium, become annual with us, and some, as the ray-grass (Lolium perenne), which with us are perennial, become annual when transplanted to more southern regions.*

The roots hitherto mentioned are fixed in the earth, but there are plants in which they are not attached to any solid body, but float in the water

there are some which grow only upon other plants - and some are almost independent of a root.

The Lemna, or duck-meat, which is found in almost every ditch, offers a ready example of the first. Its roots, which are filiform or thread-like, hang down from the surface of the water, quite unattached to any thing solid, and if you collect some good specimens in summer, when they have acquired the length of six or seven inches, and put them into a glass vessel of pure water, you will remark that these roots will present a very beautiful appearance, waving like threads of silver in the fluid. On minutely inspecting the extremity of each of these roots, you will perceive that it is thickened; and by using a magnifier, you may be able to ascertain, from your own observation, that

* "Many plants,_perennial in northern, are annual in southern regions, The heat and draught of the latter cause the roots to die away."- Link, in Botanical Tracts, London, 1805, p. 47.

this thickening is caused by a sheath which encloses the point of the root. A similar calyptra or veil is found in the roots of ferns, palms, and some other plants; and Sprengel, with some appearance of truth, supposes it to be an organ of absorption.

There is another small plant which grows in water, often floating on the surface, and frequently mixed along with the duck-weed, which at one period of its growth has floating roots, that at another are fixed in the earth and mud at the bottom. This plant is the water star-grass (Callitriche aquatica). Until flowering, it floats on the surface, and is nourished by the suspended roots; but it would appear, that before the seeds can be ripened, it is requisite that these roots should be exposed to a more substantial source of nourishment, and therefore, the flowering being over, the whole plant sinks to the bottom, strikes root, and ripens its seeds. These germinating in course, produce a young progeny of plants which rise to the surface, float there till after flowering, then, like their parent, sink to the bottom, and produce new progenies in their turn. *

"It is generally supposed to be annual, floating by means of its thick-set, broad upper leaves," till flowering, "then each flower sinks by the elongation of the top of the stem, where new ones are produced, and finally the whole herb subsides to the bottom, takes root there, ripens, and sows its seeds. The young plants soon rise to the surface, and appear to be nourished from the water by slender simple roots, from each

FLOATING ISLANDS.

31

A number of cryptogamic plants swim about at random in the waters, among which the most interesting, perhaps, in our present state of knowledge, is the sargasso, or gulf-weed of voyagers (Fucus natans), which is found in the Gulph of Florida, and some other parts of the ocean floating in masses or fields, many miles in length. No distinct root is found in this plant, and there is no doubt that it vegetates and lives long in this natant state, though originally perhaps attached to some solid substance, and not as now, a weed,

flung from the rock, on Ocean's foam to sail Where'er the surge may sweep, the tempest's breath prevail.

In like manner, the roots of land plants sometimes become detached from the banks of lakes and rivers, but falling into the water, continue to vegetate on the surface, forming floating islands. Pennant describes an island of this kind in Loch Dochart; and in lakes in Prussia, Lithuania, &c. they are found presenting the appearance of large meadows, sometimes clothed with trees. * The great American rivers, in the time of high floods, often carry down masses of their banks, covered with majestic trees and numerous climbers; and these meeting with other masses similarly swept off, form islands or rafts, which float along with the

joint of the slender branching stem, which do not reach the ground till the plant subsides as above mentioned.”— English Botany, p. 722.

* Mirbel.

stream, and sometimes carry destruction to the unwary or nocturnal voyager. "Woe (says Humboldt) to the canoes that during the night strike against these rafts of wood interwoven with lianas! Covered with aquatic plants, they resemble here (Oroonoko), as in the Mississippi, floating meadows, the chinampas of the Mexican lakes." This celebrated traveller mentions, that when the Indians wish to surprise their enemies, they tie several canoes together, and cover them with grass and branches to simulate these islands. + The Spanish smugglers at Angostura practise a similar artifice, to elude the vigilance of the custom-house officers.

The water house-leek (Pistia Stratiotes), common in American lakes and rivers, often produces a similar phenomenon. It grows in eddy water near the shore, and gradually spreads into the river, forming green plains several miles long, and sometimes a quarter of a mile broad. Its roots are long and fibrous, running into the mud; and the plant bears a general resemblance to a garden lettuce. After rains, when the rivers are suddenly raised, large tracts of these floating plains get detached,

* Pers. Nar. vol. v. p. 36.

† By a stratagem of this kind, Vasco de Gama was once attempted to be deceived. "As he was near the shore of Anchediva, he beheld the appearance of a floating isle, covered with trees, advance towards him. But his prudence was not to be deceived thus. A bold pirate, named Timoja, by linking together eight vessels full of men, and covered with green boughs, thought to board him by surprise. But Gama's cannon made seven of them fly; the eighth, loaded with fruits and provisions, he took."- Notes to Mickle's Lusiad.

SUCCULENT PLANTS.

33

Bartram

and are driven about upon the water. observes, that "these floating islands present a very entertaining prospect; for although we behold an assemblage of the primary productions of nature only, yet the imagination seems to remain in suspense and doubt; as in order to enliven the delusion, and form a most picturesque appearance, we see not only flowery plants, clumps of shrubs, old weather-beaten trees, hoary and barbed with the long moss waving from their snags, but we also see them completely inhabited and alive with crocodiles, serpents, frogs, otters, crows, herons, curlews, jackdaws, &c. There seems, in short, nothing wanted but the appearance of a wigwam and a canoe to complete the scene.'

I have said that some plants live almost independent of a root: they grow on the driest walls and rocks, the tops of houses, and other situations where no source of nourishment is presented to their radicles, and consequently they absorb their nourishment and moisture from the air, by their leaves; and as the structure of the latter is adapted for absorbing but not exhaling fluids, their substance is fleshy and full of juice, contrary to what, at a first view, we might have expected. The house-leek and sedums are examples of these among British plants; and in warmer regions the numerous species of Cactus, Mesembryanthemum and some other genera, are found flourishing best

* Bartram's Travels through Carolina, &c. p. 87.