galeopfes, as the above-mentioned author obferves, are the natural growth of black earth, and die in fand, whilft the ornithopus flourifhed in fand and perishes in a black mould.

Under air may be included the viciffitudes of folar light diffused throughout the atmosphere; which light feems to affect vegetables independently of heat, and in a manner hitherto inexplicable. All plants grow weak and flender in the confined air of hot-houfes, and much more fo if the folar light is excluded. Plants, whofe flowers are naturally the most odoriferous, if raised in a perfectly dark place, with all the advantages of warmth, moisture, &c. either do not flower at all, or bring forth flowers which have hardly any fmell. The jeffamine-tree, whilft it covers the out-fide of a wall with its fragrant flowers, is not obferved to produce a fingle one upon fuch branches as have forced their way within, even into a warm, an airy, and a light room. High hills, in different parts of the world, the Lapland crags, the Alps, Olympus, and Ararat, bring forth fimilar plants, many of which are never met with in lower grounds. These plants grow extremely quick, nature making amends for their fhortness of fummer by a continual agitation and renewal of air: they are fmall, but loaded with innumerable feeds. Removed into gardens, they grow more flowly to a larger fize, but abort or produce little fruit.

River, ftagnant, fpring, and feawaters, and watery and dry foils, have each their peculiar plants: fucculent plants rot from the quan· VOL. VII.

tity of water which many others require. It is obfervable, however, that land as well as aquatic vegetables, may be raised and fupported for a length of time by placing the little roots, wafhed clean from the earth, in water alone. It feems as if water and air, or the contents of waters, and of the atmofphere were univerfally the immediate matter which affords aliment to vegetables; as if the earth ferved only as a matrix for vegetables to keep them firm, and to preferve moisture about the roots; as if the difference of foils confifted wholly in their being more or lefs foft or compact, fo as to be eafily or difficultly penetrated by the tender roots, and in their more or lefs readily imbibing and effectually retaining water. Thus clay abforbs water very flowly and difficultly, its particles expanding in proportion as they are moistened, fo as to prevent the further progrefs of the liquor: if water be poured into a cavity made in a lump of dry clay, great part of it evaporates without being foaked in. Chalk, on the other hand, very quickly imbibes water, tranf mits it to every part of the mass, and does not eafily let it go; whilft fand fuffers it to percolate inftantaneously through the interftices of the grains, without imbibing any into its fubftance.

With regard to heat, the plants of the torrid zone require, according to Linnæus, between the fiftieth and fixtieth degree of Fahrenheit's thermometer; thofe of the temperately warm, as the fouthern parts of Europe, the Cape, Japan, China, between the thirtieth and fortieth; those of the I temperately

temperately cold, not above thirty-eight. These seem to be nearly the mean degrees of heat of the refpective climates. The plants of cold climates will not bear the heat of warm ones, any more than those of the warm can fupport the cold: fome of the Cape plants in the heat of the torrid zone, grew at firft amazingly, but foon after they loft their leaves, and were with difficulty kept alive. In this, however, there is a confiderable latitude: plants may be raised in a climate not their own, provided the difference is not very great; by degrees, they become as it were naturalized to it; if once they have produced feeds, thefe feeds are much lefs apt to mifcarry, and produce hardier plants than fuch as are brought immediately from their native country. Tobacco, from feeds of our own growth, ripens a month fooner than fuch as is raifed from foreign feeds.

It was by following nature, that the ingenious botanift above mentioned has been fo fuccefsful in bringing up the vaft variety of plants that have fallen under his care. The rubus caule unifloro foliis ternatis was fome time ago, he tells us, thought incapable of being raifed about Stockholm, till attention to its natural climate taught to keep it covered with fnow during the winter, and great part of the fpring. Mufa, the moft fpecious plant in nature, had stood near an hundred years in the Dutch botanic garden, and could not be made to blow on confidering that its native country Surinam, where the weather is dry for one half year, and rainy the next, it was kept long without water, and

afterwards kept watered abundantly: it now flowered and perfected its fruit; and by the fame management, another mufa was made to flower the next year.

He obferves, that we can easily. imitate nature in regard to earth, water, and the degree of heat; and wishes he could equally imitate her in the renewals and agitations of the air. This alfo it is in the power of art to effect. The principle that warm air afcends above cold, affords means of ob taining co nftant changes and fucfeffions of air, wherever there is warmth and cold.

Dr. Hales has applied this principle to the improvement of common hot-beds. If an aperture is made in the top of one end of the frame, and at the bottom of the other, and a defcending pipe inferted into this laft, a ftream of fresh air will pafs continually over the furface of the bed. This air may be warmed before its admiffion, by carrying the pipe that conveys it through the hot dung.

What is here effected by the heat of dung may be done in hothoufes by that of fire. A pipe, heated by the fire, and reaching to à confiderable height in the houfe, will occafion a continual circulation of the air in the houfe, that which is warmed in the pipe af cending, whilft the colder air at the bottom comes in to fupply its place, and receiving warmth from the tube, afcends in manner, and this uninterruptedly whilft the heat continues. If the lower part of the pipe is made to communicate with the external air, it will bring in fresh. If the fire-place opens immediately, or by

like

a pipe,

à pipe, into the house, the colder part of the air at the bottom will pafs off through the fire, for fire requires a large quantity of air for its fupport, whilft fresh air is brought in and warmed by the other pipe. Stronger and more fudden agitations of air, fufficient to raise a moderate wind among the plants, may be obtained occafionally by mechanic impulfe. I have made the outer and inner doors of the room, with a proper cavity between, ferve for a ventilator, the check which bounds the cavity on one fide being made of a circular curvature, that the inner door, in its motion backwards and forwards, may fit close to it all the way. The inner door is furnished with a valve at bottom, which on pulling the door backwards, receives a part of the air of the house into the cavity, and with another at the top, by which, on pufhing the door forwards, the air is forced out again with ftrength fufficient to give a confiderable shake to almoft all the plants in a large hot-house. The outer door is alfo furnished with valves, through which by a few reciprocations of the inner door, the external air is plentifully pumped in, or the internal air driven out, all the valves being made to open occafionally, outwards or inwards, and fecured on either fide with buttons.

The existence of the Fountain tree in the Canary islands ascertained, and its effects accounted for. From Glass's history of these islands.

HERE are only three fountains of water in the whole

ifland of Hierro, wherein the fountain tree grows. One of these foun tains is called Acof, which, in the language of the ancient inhabitants, fignifies river; a name, however, which does not feem to have been given it on account of its yielding much water, for in that refpect it hardly deserves the name of a fountain. More to the northward is another called Hapio; and in the middle of the island is a fpring, yielding a ftream about the thickness of a man's finger. This laft was difcovered in the year 1565, and is called the fountain of Anton Hernandez. On account of the scarcity of water, the fheep, goats, and fwine here do not drink in the fummer, but are taught to dig up the roots of fern, and chew them to quench their thirst. The great cattle are watered at those fountains, and at a place where water diftils from the leaves of a tree. Many writers have made mention of this famous tree, fome in fuch a manner as to make it ap pear miraculous: others again deny the existence of any fuch tree, among whom is father Feyjoo, a modern Spanish auther, in his Theatro Critico. But he, and thofe who agree with him in this matter, are as much mistaken as they whọ would make it appear to be miraculous. This is the only ifland of all the Canaries which I have not been in but I have failed with natives of Hierro, who, when queftioned about the existence of this tree, answered in the affirmative.

The author of the hiftory of the difcovery and conqueft has given us a particular account of it, which I fhall here relate at large.

I 2

"The

1

"The diftrict in which this tree ftands, is called Tigulahe, near to which and in the cliff, or fteep rocky afcent that furrounds the whole ifland, is a narrow gutter or gulley, which commences at the fea, and continues to the fummit of the cliff, where it joins or coincides with a valley, which is terminated by the steep front of a rock. On the top of this rock grows a tree called in the language of the ancient inhabitants, Garfe, Sacred or Holy Tree, which for many years has been preferved found, entire, and fresh. Its leaves conftantly distil fuch a quantity of water as is fufficient to furnifh drink to every living creature in Hierro; nature having provided this remedy for the drought of the ifland. It is fituated about a league and a half from the fea. Nobody knows of what fpecies it is, only that it is called Til. It is diftinct from other trees, and stands by itfelf; the circumference of the trunk is about twelve fpans, the diameter four, and in height from the ground to the top of the higheft branch, forty fpans the circumference of all the branches together is one hundred and twenty feet. The branches are thick and extend'ed; the loweft commence about the height of an ell from the ground. Its fruit resembles the acorn, and taftes fomething like the kernel of a pine-apple, but is fofter and more aromatic. The leaves of this tree resemble thofe "of the laurel, but are larger, wider, and more curved; they come forth in a perpetual fucceffion, fo that the tree always remains green. Near to it grows a thorn which faftens on many of its branches

and interweaves with them: and at a small distance from the Garfe are fome beech trees, brefos, and thorns. On the north fide of the trunk are two large tanks or cifterns, of rough stone, or rather one ciftern divided, each half being twenty feet fquare, and fixteen fpans in depth. One of these contains water for the drinking of the inhabitants, and the other that which they use for their cattle, wafhing, and fuch-like purposes. Every morning, near this part of the island, a cloud, or mift arifes from the fea, which the south and easterly winds force against the fore-mentioned fteep cliff; fo that the cloud having no vent but by the gutter, gradually afcends it, and from thence advances flowly to the extremity of the valley, where it is stopped and checked by the front of the rock which terminates the valley, and then refts upon the thick leaves and widespreading branches of the tree, from whence it diftils in drops during the remainder of the day, until it is at length exhaufted, in the fame manner that we fee water drip from the leaves of trees, after a heavy shower of rain. This diftillation is not peculiar to the Garfe, or Til, for the brefos, which grow near it, likewife drop water; but their leaves being but few and narrow, the quantity is fo trifling, that though the natives fave fome of it, yet they make little or no account of any but what diftils from the Til, which, together with the water of fome fountains, and what is faved in the winter feafon, is fufficient to serve them and their flocks. This tree yields moft water in thofe years when the

Levant,

Levant, or easterly winds have prevailed for a continuance'; for by thefe winds only the clouds or mifts are drawn hither from the fea. A perfon lives on the fpot near which this tree grows, who is appointed by the council to take care of it and its water, and is allowed a houfe to live in, with a certain falary. He every day diftributes to each family of the district seven pots or veffels full of water, befides what he gives to the principal people of the island.”

Whether the tree which yields water at this present time, be the fame as that mentioned in the above defcription, I cannot pretend, to determine; but it is probable there has been a fucceffion of them; for Pliny, defcribing the Fortunate ifland, fays, "In the mountains of Ombrion are trees resembling the plant Ferula, from which water may be procured by preffure. What comes from the black kind is bitter, but that which the white yields is fweet and potable.

Trees yielding water are not peculiar to the island of Hierro, for travellers inform us of one of the fame kind on the iftand of St. Thomas, in the bight or gulph of Guiney. In Cockburn's voyages we find the following account of a dropping tree, near the mountains of Vera Paz, in America.

"On the morning of the fourth day we came out on a large plain, where were great numbers of fine deer, and in the middle ftood a tree of unusual fize, fpreading its branches over a vaft compafs of ground. Curiofity led us up to it; we had perceived, at fome diftance off, the ground about it to be wet, at which we began to

be fomewhat furprized, as well knowing there had no rain fallen for near fix months paft, according to the certain courfe of the feafon in that latitude; that it was impoffible to be occafioned by the fall of dew on the tree, we were convinced, by the fun's having power to exhale away all moisture of that nature a few minutes after its rifing. At last, to our great amazement as well as joy, we saw water dropping, or as it were diftilling, fast from the end of every leaf of this wonderful (nor had it been amifs if I had faid miraculous) tree; at leaft it was fo with refpect to us, who had been labouring four days through extreme heat, without receiving the leaft moisture, and were now almost expiring for the want of it.

We could not help looking on this as liquor fent from heaven to comfort us under great extremity. We catched what we could of it in our hands, and drank very plentifully, of it, and liked it fo well, that we could hardly prevail with ourselves to give over., A matter of this nature could not but excite us to make the ftricteft obfervations concerning it, and accordingly we ftaid under the tree near three hours, and found we could not fathom its body in five times. We observed the foil where it grew to be very ftony; and upon the niceft enquiry we could afterwards make, both of the natives of the country and the Spanish inhabitants, we could not learn there was any fuch tree known throughout New Spain, nor perhaps all America over; but I do not relate this as a prodigy