ROO
pendicularly down into the earth, the greater part have vifi- ble fibres running horizontally from them in great num- bers, and even thofe which feem to have none, are not truly without them, they being only more fine and there- fore lefs diftinguifliable by the eye.
The horizontal roots iiTuing from the main body of the root feem to the eye to befhort, and reach only a little way, but they in reality extend many times farther than they feem to do, often fpreading to the diftance of many yards, after their cxtream finenefs and earthy colour makes them imperceptible to the eye. Mr. Tull has made experiments of this kind, and found that a turnep, which is a plant whoferoot feems to have as few and thofe as fbort fibres growing from its main ftem as any. yet has fuch as when the ground about it is properly moved by digging, extend to the diftance of fix feet every way. The diftance to which thefe fibres of the roots of plants extend may be difcovered by trials with fait ; the common garden plants will not live, if their roots reach to a place where there is fait; therefore if feveral plants of the fame kind be planted in different parts of the fame bed of earth, and a trench dug round each at different diftances, and fait buried in this trench, ft will be feen by the decaying of fome of thefe plants, and the thriving of others, according to the diftance at which the fait lies, which of them has reached it with their roots, and which have not ; that is, which fait is placed at a diftance, to which the plants cannot extend their roots, and which is the fartheft place to which they ■do. If a furrow be cut in the ground of the depth of nine inches, and at the diftance of a yard from a turnep root. that root will extend its horizontal fibres to this diftance, at the depth of fix inches or thereabout from the furface but when they are come thus far they will defcend perpen Uicularly below the level of the bottom of the furrow, and when they have pafled it, they will rife to the level of the others on the oppofite fide, and extend to the diftance of a yard beyond it. This could fcarce be conceived of a plant which feems to have fo few horizontal fibres as the turnep. but experiment has (hewn it to be a certain fa£t. This is not peculiar to the turnep ; for all other plants do it on occafion. The open mould being the natural foil for them to draw nourishment from, if they defcend perpen dicularly out of this to avoid expofing themfelves to the open air where there is a cut or ditch, as foon as they have paffed this, they always mount upwards again to enjoy the vegetable mould again at their proper depth : this is the reafon of what feems fo ftrange a thing in the turnep fibres as their rifing after they had pafled the furrow. The roots of a common thorn hedge may be obferved to run horizontally in their natural direction, and if they come to a ditch they will defcend perpendicularly till lower than its bottom, and then running acrofs it, they will immediately mount again toward the furface, and extend themfelves horizontally at the depth of eight or ten inches to a great diftance : on opening the earth at five feet di- ftance from the ditch, the roots will be found tolerably large, and none of them reaching deeper than the common mould, which feldom is above a fpade deep. Mr. Tull mentions a very extraordinary inftance of the fpreading of the roots of trees in that of a witch elm ; a chalk pit contiguous to a barn, the area of which was about forty perch of ground, was made clean and fwept, fo that it could plainly be feen that there was no vegetable matter about it, any more than in the floor of the barn i ftraw was thrown from thence into the pit for cattle to lie on, and about three years after the pit was cleanfed, the dung made in it being taken up ; *he bottom of the pit, and the top of the chalk were at this time covered with roots, and thefe were found to come from a witch elm, cf not more than five or fix yards in height, which was about five yards above the area of the pit, and eleven yards from it ; fo that in three years the roots of this tree had extended themfelves to eight times the length of the body of the tree, beyond the extremity of the old roots, at eleven yards diftance from the bottom of the trench, whence the original roots proceed. The annual encreafe of the length of the roots in this cafe was about three times as much as the whole length of the tree. The vegetable mould which lies ufually from the furface, to about a foot deep, being a proper place for the roots of trees, they will rife into it, tho* the unfkilful hand of man plant them deeper. Thus in an orchard where the trees are fet too deep, their roots all afcend till they come to a pro- per fcene of nourifhment ; but if the ground be moift there is a difadvantage in this, for the roots pairing thro' a watery place are chilled, and the circulation retarded. The generality of the world fuppofe, that the horizontal roots of plants are much fhorter than they really are, be- caufe they fee that they are pretty taper near the roar, and feem to come to a point very foon : by this obfervation they conclude that they diminifti on in the fame propor- tion that they do there, and confequently that they very fcon come to an end. But by this means they calculate their length at lefs than en* twentieth part of what it reallv SuppC, Vol. II.
ROO
is ; for the truth is, that after the length of a few inches from the main root, they are not difcemibly taper, but pafs on in the fame bignefs to their very ends. This may be (cen at any time in the roots of plants growing in water, and with care in the tracing them it may alfo be feen in thofe which grow in the earth ; but the reafon why it is not commonly feen in thefe, is that they generally break off in the taking up about the part where they grow taper. Many plants which feem to have only large naked roots have thefe horizontal ones, which tho' fmal! are branched out into many iefler fibres, and convey a great deal of nourifliment to the plant, and that from a great diftance. If a common carrot be taken up and examined, there will be found many fine fibres, like hairs growing from its fides: each of thefe examined with a microfcope, will be found to be a root not going taper, but all the way of the fame big- nefs broken off at the end, and fending numerous fibres from its fides ; all thefe are extended to fome length, and then appear broken off as the other ; and it is very pro- bable from what is known to be the cafe in the turneps, that this horizontal root is in its natural ftate extended four, five, or fix feet from the carrot, ail the way of the fame length, and all the way fending out its lateral {hoots or fibres which run upwards and downwards the whole fpace of the ten or twelve inches of vegetable mould. If fo, from what a diftance every way, and by what an im- menfe number of channels does this plant receive nourifh- ment ?
The ufe of digging the earth to a great diftance every way from the roots of fitch plants as are defired to thrive well, is evident from this : for thefe tender roots which in ao open mould will run to fo many feet diftance, are pinch- ed up, and deftroyed when they come into a hard and undug earth. The advantage of having clear fpaces be- tween plants cultivated for ufe, is alfo plain from this, fince they all have roots, tho' imperceptible to us, which occupy thofe fpaces, and draw nourifliment from them. Many plants are of a fort of amphibious nature, and grow as well in water as on land ; the perficaria falicis folio, or willow leaved arfmart, called when in the water, the long leaved pond-weed, is an inftance of this kind. This in the water and on the land makes fo different an ap- pearance, that the old botanifts have taken it for two dif- ferent plants. The roots of this, and of all other fuch plants, are much longer when they grow on land, than when in water.
The fecrets of vegetation as carried on by roots, and the ufes one part of the root is of to the other parts, are yet far from being underftood to perfection. We know in- deed that all roots imbibe moifture from the earth, but it alfo appears, that they part with that moifture again in the form of water, as they received it without carrying it all up into the body of the plant on certain occafions. If a piece of flourifhing mint in a water glafs be fo contrived, that while the roots from one joint are all immerfed in water, thofe of an upper joint he received into a box, and laid all at one corner of it, and the box filled with fand dryed at the fire ; after a nights ftanding, the water in the glafs will be found fenfibly decreafed, and the fand at that comer of the box where the roots of the mint are, will be found very wet, while all the reft remains dry. This water which has thus wetted the fand, muft have been received into the lower roots, and from thence conveyed to the upper ones, and they muft have again delivered it out into the fand, inftead of carrying it up into the body of the plant. Let a trough of earth be prepared of two feet in length, and let a ftrong fhoot of mint be fet in a glafs of water at each end of the trough, and while half the roots of each are placed in the water, let the other half be laid in the trough and covered with dry earth in powder j this dry earth will foon become moift, and the roots will fhoot out bevond its furface. Thefe are to be covered with foft earth as they appear, till the trough will hold no more ; the whole trough will thus be foon filled with the roots of thefe two fhoots of mint, and thofe roots which rife to the furface, and are not covered, will be feen to bend down their points and enter the earth again. 7'hefe mints grow greatly fafter than thofe which arc planted either in water alone, or in water with earth in it ; and the cartk in the trough will always be found thoroughly moi- ftcned, tho' no water is put to it, except what arifes fiom the lower roots, and is carried to thefe upper ones, which are placed in the earth. The quantity of water thus feat up by the lower roots, and thrown into the earth above by the upper ones, is more than a tlioufand times the whole weight of the plants, and feems to have never mixed itfclf with the juices of the plant at all, but to have been eva- cuated pure water as it was received without ever going any higher than the upper roots.
The glades in thefe experiments need very frequent fup- plies, a day or two being fufticient to drain them ; but what is remarkable is, that if they are fuffered to be with- out water in the glafles, they will not dry up or wither, but the roots below, as well as the plant above, will be X j i kept
