But such roots as I call horizontal (except of trees) have seldom any of their branchings deeper than the surface or staple of the earth, that is commonly moved by the plough or spade.
The tap-root commonly runs down single and perpendicular, reaching sometimes many fathoms below.
In this manner descends the first root of every seed, but of corn very little, if at all, deeper than the earth is tilled.
These first seed-roots of corn die as soon as the other roots come out near the surface, above the grain, and therefore this first is not called a tap-root ; but yet some of the next roots that come out near the surface of the ground, always reach down to the bottom of the pulverized staple ; as may be seen, if you carefully examine it in the spring time ; but this first root in saint-foin becomes a tap-root.
This, though it goes never so deep, has horizontal ones passing out all round the sides, and extend to several yards distance from it, after they are, by their minuteness and earthy tincture, become invisible to the naked eye.
A piece or plot dug and made fine in whole hard ground, the end
The manner of this hoeing must be at first near the plants with a spade, and each time afterward a foot further distance, till all the earth be once well dug ; and if weeds appear where it has been so dug, hoe them out shallow with the hand-hoe. But dig all the piece next the out lines deep every time, that it may be the finer for the roots to enter, when they are permitted to come thither.
If these turnips are all gradually bigger, as they stand nearer to the end B, it is a proof they all extend to the outside of the piece, and the turnip 20, will appear to draw nourishment from six feet distance from its centre.
But if the turnips 16, 17, 18, 19, 20, acquire no greater bulk than the turnip 15, it will be clear that their roots extend no further than those of the turnip 15 do, which is but about four feet.
By this method the distance of the extent of roots of any plant may be discovered.
There is also another way to find the length of roots, by making a long narrow trench, at the distance you expect they will extend to, and fill it with salt ; if the plant be killed by the salt, it is certain that some of the roots enter into it.
What put me upon this method was an observation of two lands, or ridges, drilled with turnip in rows, a foot asunder, and very even in them ; the ground, at both ends and one side was hard and unploughed, the turnips not being hoed, were very poor, small, and yellow, except the three outside rows, B, C, D, which stood next to the land (or ridge) E, which land being ploughed and harrowed at the time the land A ought to have been hoed, gave a dark flourishing colour to these three rows ; and the turnips in the row D, which stood furthest off from the new ploughed land E, received so much benefit from it as to grow twice as big as any of the more distant rows. The row C, being a foot nearer to the new ploughed land, became twice as large as those in D ; but the row B, which was next to the land E, grew much larger yet.
A like observation to this on the land E, has been made in several turnip-fields of divers farmers, where lands adjoining to the turnips have been well tilled, all the turnips of the contiguous lands that were within three of four feet, or more, of the newly pulverised earth, received as great, or greater increase, in the same manner as my rows B, C, D, did ; and what is yet a greater proof of the length of roots and of the benefit of deep hoeing, all these turnips have been well hand-hoed ; which is a good reason why the benefits of the deep pulverisation should be perceivable at a greater distance from it than mine, because my turnips not being hoed at all, had not strength to send out their roots through so many feet of unpulverised earth, as these can through their earth pulverised by the hoe, though but shallowly.
This observation, as it is related to me, (I being unable to go far enough to see it myself,) sufficiently demonstrates the mighty difference there is between hand-hoeing and horse-hoeing.
F is a piece of hard whole ground, of about two perches in length, and about two or three feet broad, lying betwixt those two lands, which had not been ploughed that year ; it was remarkable, that during the length of this interjacent hard ground, the rows B, C, D, were as small and yellow as any in the land.
The turnips in the row D, about three feet distant from the land E, receiving a double increase, proves that they had as much nourishment from the land E, as from the land A, wherein they stood ; which nourishment was brought by less than half the number of roots of each of these turnips.
In their own land they must have extended a yard all round, else they could not have reached the land E, wherein it is probable these few roots went more than another yard, to give each turnip as much increase as all the roots had done in their own land.
Except that it will hereafter appear, that the new nourishment taken at the extremities of the roots in the land E, might enable the plants to send out more new roots in their own land, and receive something more from thence.
The row C, being twice as big as the row D, must be supposed to extend twice as far ; and the row B, four times as far, in proportion as it was of a bulk quadruple to the row D.
A turnip has a tap-root, from whence all these horizontal roots are derived. And it is observable, that betwixt these two lands, there was a trench, or furrow, of about the depth of nine or ten inches, where these roots must descend first, and then ascend into the land E, but it must be noted, that some small quantity of earth was, by the harrowing, fallen into this furrow, else the roots could not have passed through it.
Roots will follow the open mould*, by descending perpendicularly, and mounting again in the same manner ; as I have observed the roots of a hedge to do that have passed a steep ditch two feet deep, and reached the mould on the other side, and there fill it ; and digging five feet distant from the ditch, found the roots large, through this mould was very shallow, and no roots below the good mould.
* A chalk-pit contiguous to a barn, the area of which being about forty perch of ground, was made clean and swept ; so that there was not the appearance of any part of a vegetable, more than in the barn's floor straw was thrown from thence into the pit for cattle to lie on ; the dung made thereby was hauled away about three years after the pit had been cleansed, when, at the bottom of it, and upon the top of the chalk, the pit was covered all over with roots, which came from a witch-elm, not more than five or six yards in length from top to bottom, and which was about five yards above, and eleven yards from the area of the pit ; so that in three years the roots of this tree extended themselves eight times the length of the tree, beyond the extremities of the old roots, at eleven yards distance from the body. The annual increased length of the roots was near three times as much as the height of the tree.
I am told an objection has been made from hence against the growth of a plant being in proportion to the length of its roots ; but when the case is fully stated, the objection may vanish. This witch-elm is a very old decayed stump, which is here called a stagger, appearing by its crookedness to have been formerly a plasher in an old white-thorn hedge wherein it stands. It had been lopped many years before that accidental increase of roots happened ; it was stunted, and sent out poor shoots ; but in the third year of these roots, its boughs being most of them horizontally inclined, were observed to grow vigorously, and the leaves were broad and of a flourishing colour ; at the end of the third year all these roots were taken away, and the area being a chalk rock lying uncovered round the place where the single root, that produced all these, came out of the bank, no more roots could run out on the bare chalk, and the growth of the boughs has been but little since.
Wheat drilled in double rows in November, in a field well tilled before planting, looked yellow when about eighteen inches high ; at two feet distance from the plants, the earth was hoe-ploughed, which gave such nourishment to them, that they recovered their health, and changed their sickly yellow to a lively green colour.
So in an orchard, where the threes are planted too deep below the staple or good mould, the roots, at a little distance from the stem, are all as near the upper superficies of the ground as of those trees which are planted higher than the level of the earth's surface. But the damage of planting a tree to low in moist ground is, that in passing through this low part standing in the sap is chilled, and its circulation thereby retarded.
One cause of people's not suspecting roots to extend to the twentieth part of the distance, which in reality they do, was from observing these horizontal roots, near the plant, to be pretty taper ; and if they did diminish on in proportion to what they do there, they must soon come to an end. But the truth is, that after a few inches, they are not discernibly taper, but pass on to their ends very nearly of these same bigness ; this may be seen in roots growing in water, and some other, though with much care and difficulty.
In pulling up the aforementioned turnips, their roots seemed to end at a few inches distance from the plants, they being further off, too fine to be perceived by ordinary observation.
I found an extreme small fibre on the side of a carrot, much less than a hair, but through a microscope it appeared a large root, not taper, but broken off short at the end, which, it is probable, might (before broken off) have extended nearly as far as the turnip-roots did. It had many fibres growing out of it ; and I have seen that a carrot will draw nourishment from a great distance, though the roots are almost invisible where they come out of the carrot itself.
By the piece F may be seen that those roots cannot penetrate, unless the land be opened by tillage, &c.
And it is very likely and may be proved by another method, that as roots are but as guts inverted, they do bear, perhaps, that proportion to the stem or stalks of plants, as guts do to the bodies of animals*, viz. several times longer than the stalks.
* An animal has but one gut, though its parts be distinguished by several names ; an the greater number of roots a plant has, the less length of them will suffice.
As animals of different species have their guts bearing different proportions to the length of their bodies ; so it is probable different species of plants may have their roots as different. But if those which have shorter roots have more in number, and having set down the means how to know the length of them in the earth, I leave the different lengths of different species to be examined by those who will take the pains of more trials. This is enough for me, that there is no plant commonly propagated, but what will send out its roots far enough, to have the benefit of all the hoed spaces or intervals I in the following chapters allot them, even though they should not have roots so long as their stalks or stems (roots of amphibious plants grow longer when in earth than when in water.)
And this great length of roots will appear very reasonable, if we compare the largeness of leaves (which are the parts ordained for excreting) with the smallness of the capillary roots, which must make up in length or number what they want in bigness, being destined to range far in the earth to find out a supply of matter to maintain the whole plant ; whereas the chief office of the stalks and leaves is only to receive the same, and to discharge into the atmosphere such part thereof as is found unfit for nutrition ; a much easier task than the other, and consequently fewer passages suffice, these ending in an obtuse form ; for otherwise the air would not be able to sustain the stalks and leaves in their upright posture ; but the roots, though very weak and slander, are easily supported by the earth, notwithstanding their length, smallness, and flexibility.
Plants have no stomach, nor ęsophagus, which are necessary to convey the mass of food to an animal ; which mass being exhausted by the lacteals, is eliminated by way of excrements ; but the earth itself being that mass to the guts (or roots) of plants, they have only fine recrements, which are thrown off by the leaves.
In this animal and vegetable bodies agree, that guts and roots are both injured by the open air ; and nature has taken an equal care that both may be supplied with nourishment, without being exposed to it. Guts are supplied from their insides, and roots from their outsides.
All the nutriment, or pabulum, which guts receive for the use of an animal, is brought to them ; but roots must search out and fetch themselves all the pabulum of a plant ; therefore a greater quantity of roots, in length or number, is necessary to a plant, than of guts to an animal.
All roots are as the intestines of animals, and have their mouths or lacteal vessels, opening on their outer spongy superficies, as the guts of animals have theirs opening in their inner spongy superficies.
The animal lacteals take in their food by the pressure that is made from the peristaltic motion, and that motion caused by the action of respiration, both which motions press the mouths of the lacteals against the mass or soil which is within the guts, and bring them into closer contact with it.
Both these motions are supplied in roots by the pressure occasioned by the increase of their diameters in the earth, which presses their lacteal mouths against the soil without. But in such roots as live in water, a pressure is constantly made against the roots by the weight and fluidity of the water ; this presses such fine particles of earth it contains, and which come into contact with their mouths, the closer to them.
And when roots are in a tilled soil, a greater pressure is made against them by the earth, which constantly subsides and presses their food closer and closer, even into their mouths, until itself becomes so hard and close, that the weak sorts of roots can penetrate no further into it, unless re-opened by new tillage, which is called hoeing.
The colour of roots being different from that of leaves, and some other external parts of a plant, is no more an argument against the circulatiion of the sap, than the colour of the guts, being different from that of the lungs, and other parts of an animal body, is an argument against the circulation of the blood.
As far as I can yet discover, all roots, properly so called, are
white ; and the red carrot, when it stands for seed, sends out in the spring, from all parts of it, fibrous roots as white as those of any other plant. The white colour proceeds from the chyliferous vessels, or rather from the waterish, wheyish chyle contained in them.
When a good number of single-mint stalks had stood in water until they were well stocked with roots from their two lower joints, and some of them three joints, I set one into a mint-class, marked A, full of salt water : this mint A became perfectly dead within three days.
Another mint, marked B, I put into a glass of fair water, but I immersed one string of its roots, being brought over the top of that glass, into another glass of salt water, contiguous to the top of the other glass ; this mint died also very soon.
Of another, marked C, (standing in a glass of water and earth till it grew vigorously,) I tied one single root into a bag which held a spoonful of dry salt, adjoining to the top of the glass, which killed this strong mint also. I found that this salt was soon dissolved, though on the outside of the glass, and though no water reached so high as to be within two inches of the joint which produced this root. The leaves of all these were salt as brine to the taste.
To another, marked D, I put an upper root into a small glass of ink instead of a bag of salt, in the manner above mentioned ; this plant was killed by some of the ink ingredients. The blackness was not communicated to the stalk or leaves, which inclined rather to a yellowish colour as they died, which seemed owning to the copperas.
I made a very strong liquor with water, and bruised seeds of wild garlic, and filing a glass therewith, placed the top of it close to the
top of another glass, having in it a mint, marked E, two or three of the upper roots of which put into this stinking liquor, full of the bruised seeds, and there remaining, it killed the mint in some time, but it was much longer in dying than the others were with the salt and ink. It might be because these roots in the garlic were very small, and did not bear so great a proportion to their whole system of roots as the roots by which the other mints were poisoned did to theirs.
When the edges of the leaves began to change colour, I chewed many of them in my mouth, and found at first a strong aromatic flavour of mint, but that was soon over ; and then the nauseous taste of garlic was very perceptible to my palate.
I observed that when mint F had stood in a glass of water until it seemed to have finished its growth, the roots being about a foot long and of an earthy colour, after putting in some fine earth which sunk down to the bottom, there came from the upper joint a new set of white roots, taking their course on the outside of the heap of old roots downwards, until they reached the earth at the bottom, and then, after some time, came to the same earthy colour with the old ones.
The mint G being well rooted from two joints, about four inches asunder, I placed the roots of the lower joint in a deep mint glass, having water at the bottom, and the roots of the upper joint in a square box, contrived for the purpose, standing over the glass and having a bottom that opened in the middle, with a hole that shut together close to the stalk, just below the upper joint ; then laying all these upper roots to one corner of the box, I filled with sand dried in a fire shovel, and found that, in one night's time, the roots of the lower joint which reached the water at the bottom of the glass, had drawn it up, and imparted so much thereof to those roots in the box above, that the sand, at that quarter where they lay, was very wet, and the other three corners dry. This experiment I repeated very often, and it always succeeded as that did.
And for the same purpose I prepared a small trough, about two feet long, and placed a mint-class under each end of the trough ; over each glass, I placed a mint, with half its roots in the glass the other half in the trough : the mints stood just upon the ends of the trough. Then I covered these roots with pulverised earth, and kept the glasses supplied with water ; and as often as the white fibrous roots shot through the earth, I threw on more earth, until the trough would hold no more, and still the white fibres came through, and appeared above it, but all seemed, as I saw by the help of a coarse microscope, to turn, and when they came above ground, their ends entered into it again. These two mints grew thrice as large as any other mints I had, which were many, that stood in water, and much larger than those which stood in water with earth in it ; they being all of an equal bigness when set in, and set at the same time. Though these two standing in my chamber never had any water in their earth, but what those roots, which reached the water in the glasses, sent up to the roots which grew in the trough. The vast quantity of water these roots sent up being sufficient to keep all the earth in the through moist, though of a thousand times greater quantity than the roots which watered it, makes it probable that the water passed out of the roots into the earth, without mixing at all with the sap, or being altered to any degree. The earth kept always moist, and in hot weather there would not remain a drop of water in the glasses, when they had not been fresh supplied in two days and one night ; and yet these roots in the glasses were not dried, though they stood sometimes a whole day and night thus in the empty glasses. These two mints have thus lived all one summer, and are marked HH.
Remarks on the Mints, &c. - Though the vessels of marine plants be someways fortified against the acrimony of salt, as sea-fish are, yet the mints A, B, C, all show that salt is poison to other plants.
The reason why the salts in dung, brine, or urine, do not kill plants in the field or garden is, that their force is spent in acting
upon and dividing the parts of earth : neither do these salts, or at least any considerable quantity of them, reach the roots.
I tried salt to many potatoes in the ground, being undermined, and a few of their roots put into a dish of salt water, they all died sooner or later, according to the bigness, and to the proportions the quantity of salt applied did bear to them.
By the mints B, C, D, E, it appears that roots make no distinctions in the liquor they imbibe, whether it be for their nourishment or destruction. And that they do not insume what is disagreeable, or poison to them, for lack of other sustenance, since they were very vigorous, and well fed in the glasses at the time when the most inconsiderable part of their number had the salt, garlic, and ink offered to them.
The mint F shows, that when new earth is applied to the old roots, a plant sends out new roots on purpose to feed on it ; and that the more earth is given it, the more roots will be formed, by the new vigour the plant takes from the addition of earth. This corresponds with the action of hoeing ; for every time the earth is moved about roots, they have a change of earth which is new to them.
The mint G proves, that there is such a communication betwixt all the roots, that when any of them have water, they do impart a share thereof to all the rest : and that the root of the lower joint of this mint had passages, or vessels, leading from them, through the stalk, to the roots of the upper joint ; though the clear stalk (through which it must have passed), that was betwixt these two joints, was several inches in length.
This accounts for the great produce of long tap-rooted plants, such as Lucerne and St. Foin, in very dry weather ; for the earth, at a great depth, is always moist. It accounts also for the good crops we have in dry summers, upon land that has a clay bottom ; for there the water is retained a long time, and the lower roots of plants which reach it do, like those of this mint, send up a share to all the higher roots.
If those roots of a plant, which lie at the surface of the ground, did not receive moisture from other roots which lie deeper, they could be of no use in dry weather. But it is certain, that if this dry surface be moved or dunged, the plant would be found to grow the faster, though no rain fall ; which seems to prove, both that the deep roots communicate to the shallow a share of their water, and receive in return from them a share of food, in common with all the rest of the plant, as in mints F, G, HH, they did.
They receive it by their capillary sap vessels, after it has been purified and prepared by the leaves fit for nourishing all parts of the plant.
The two mints marked HH, show that when the upper roots have moisture, (as they had in the earth in the trough, carried thither first by the lower roots,) they impart some of it to the lower, else they could not have continued plump and fresh, as they did for twenty-four hours in the empty glass. And I have since observed therm to do so, in the cooler season of the year, for several weeks together, without any other water than what the upper roots conveyed to them from the moist earth above in the trough. I know not what time these roots might continue to be supplied thus in the hot weather, because I did not try any longer, for fear of killing them.
It is certain, that roots and other chyle vessels of a plant have a free communication through all their cavities, and the liquor in them will run towards that part where there is least resistance ; and such is that which is the most empty, whether it be above or below ; for there are no valves that can hinder the descent or ascent of liquor in these vessels, as appears by the growing of a plant in an inverted posture.
But it must be noted, that the depth of the glass protected the roots therein from the injury of the motion of the free air, which would have dried them if they had been out of the glass.
In this trough is shown most of the hoeing effects, viz. that roots, by being broken off near the ends, increase their number, and send out several where one is broken off.
That the roots increase their fibres every time the earth is stirred about them.
That the stirring the earth makes the plants grow the faster.
The mint discharging such a vast quantity of water into the earth in the trough, shows that there are passages by which the roots do, as it were, spew out what is superfluous, and would surfeit the plant if it entered into the sap in too great abundance, more and faster than it could be purified by the leaves.
Whether this water, which is so soon returned out of the roots, be at all altered during its short stay there, I cannot say, until I see the consequence of some experiments, which will, I believe, inform me, viz., Half the fibrous root of garlic set in water, the other half in a trough of flour above it, as those of the mint were ; if the water the under-garlic roots send to the upper be spewed out into the flour of a garlic taste, then we know it is altered, otherwise conclude it is not altered. A mint is not of flavour strong enough to prove this.
Though the earth and water by passing twice through the pores of garlic roots should possibly acquire some small alteration, it would be no proof of its being converted into sap ; for if you steep this strong scented plant in a considerable quantity of water, it will all have a tincture of its stench from its effluvia, and yet nobody will believe such water is become sap ; yet I know not whether there are enough of those effluvia in its fibrous roots, not having prosecuted that experiment. And now upon further consideration, I think mint a much fitter plant than garlic, to show the difference there is between chyle and sap, because its effluvia are not so strong, and the fibrous roots of the mint may be drawn out at every joint of the stem. The chyle may be had from fibrous roots near the top, which enters at the roots at its bottom.
Note. It is best to lop off the tender top of the mint, in order to make the stem the stronger, to afford the more high roots, when set in water ; for no root will ever come out of it in the open air.