Capital SSince the most immediate Use of Agriculture, in feeding Plants, relates to their Roots, they ought to be treated of in the first Place.

Roots are very different in different Plants: But ’tis not necessary here to take notice of all the nice Distinctions of them; therefore I shall only divide them in general into two Sorts, viz. Horizontal-Roots, and Tap-Roots, which may include them all.

All have Branchings and Fibres going all manner of ways, ready to fill the Earth that is open.

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 mov’d by the Plough or Spade.

The Tap-Root commonly runs down Single and Perpendicular[1] reaching sometimes many Fathoms below.

This (tho’ 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 earthly Tincture, become invisible to the naked Eye.

A Method how to find the Distance to which Roots extend Horizontally.

Pl. 6. Fig. 7. Is a Piece or Plot dug and made fine in whole hard Ground, the End A 2 Feet, the End B 12 Feet, the Length of the Piece 20 Yards; the Figures in the middle of it are 20 Turneps, sown early, and well ho’d.

The manner of this Hoing must be at first near the Plants, with a Spade, and each time afterwards, a Foot farther 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 Turneps are all gradually bigger, as they stand nearer to the End B, ’tis a Proof they all extend to the Outside of the Piece; and the Turnep 20 will appear to draw Nourishment from six Feet Distance from its Centre.

But if the Turneps 16, 17, 18, 19, 20, acquire no greater Bulk than the Turnep 15, it will be clear, that their Roots extend no farther than those of the Turnep 15 does; which is but about 4 Feet.

By this Method the Distance of the Extent of Roots of any Plant may be discover’d.

What put me upon this Method was an Observation of two Lands (or Ridges) drill’d with Turneps in Rows, a Foot asunder, and very even in them; the Ground, at both Ends, and one Side, was hard and unplow’d; the Turneps not being ho’d, 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 plow’d and harrow’d, at the time the Land A ought to have been ho’d, gave a dark flourishing Colour to these three Rows; and the Turneps in the Row D, which stood farthest off from the new-plow’d 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-plow’d Land, became twice as large as those in D; but the Row B, which was next to the Land E, grew much larger yet[2].

F Plate 6. is a Piece of hard whole Ground, of about two Perch in Length, and about two or three Feet broad, lying betwixt those two Lands, which had not been plow’d that Year; ’twas 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 Turneps in the Row D, about three Feet distant from the Land E, receiving a double Increase, proves 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 Turneps.

In their own Land they must have extended a Yard all round, else they could not have reach’d the Land E, wherein ’tis probable these few Roots went more than another Yard, to give each Turnep 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 suppos’d 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 Turnep has a Tap-Root, from whence all these Horizontal Roots are deriv’d.

And ’tis 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, fall’n into this Furrow, else the Roots could not have pass’d thro’ it.

Roots will follow the open Mould[3], by descending perpendicularly, and mounting again in the same manner: As I have observ’d the Roots of a Hedge to do, that have pass’d a steep Ditch two Feet deep, and reach’d the Mould on the other side, and there fill it; and digging Five Feet distant from the Ditch, found the Roots large, tho’ this Mould was very shallow, and no Roots below the good Mould.

So in an Orchard, where the Trees 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 too low in moist Ground is, that in passing thro’ this low Part, standing in Water, the Sap is chill’d, and its Circulation thereby retarded.

One Cause of Peoples 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 the same Bigness; this may be seen in Roots growing in Water, and in some other, tho’ with much Care and Difficulty.

In pulling up the aforemention’d Turneps, their Roots seem’d to end at few Inches Distance from the Plants, they being, farther off, too fine to be perceiv’d by ordinary Observation.

I found an extreme small Fibre on the Side of a Carrot, much less than a Hair; but thro’ a Microscope it appear’d a large Root, not taper, but broken off short at the End, which it is probable might have (before broken off) extended near as far as the Turnep Roots did. It had many Fibres going out of it, and I have seen that a Carrot will draw Nourishment from a great Distance, tho’ the Roots are almost invisible, where they come out of the Carrot itself.

By the Piece F Plate 6. may be seen, that those Roots cannot penetrate, unless the Land be open’d by Tillage, &c.

As Animals of different Species have their Guts bearing different Proportions to the Length of their Bodies; so ’tis 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 examin’d 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 ho’d Spaces or Intervals I in the following Chapters allot them, even tho’ they should not have Roots so long as their Stalks or Stems.

And this great Length of Roots will appear very reasonable, if we compare the Largeness of the Leaves (which are the Parts ordain’d for Excretion) with the Smalness of the Capillary Roots, which must make up in Length or Number what they want in Bigness, being destin’d 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, tho’ very weak and slender, are easily supported by the Earth, notwithstanding their Length, Smalness, and Flexibility.

Plants have no Stomach, nor Oesophagus, 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 supply’d with Nourishment, without being expos’d to it. Guts are supply’d 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 caus’d 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 supply’d in Roots by the Pressure occasion’d 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 till’d Soil, a great 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 farther into it, unless re-open’d by new Tillage, which is call’d Hoing.

When a good Number of Single-Mint Stalks had stood in Water, until they were well stock’d with Roots from their two lower Joints, and some of them from three Joints, I set one in a Mint-Glass full of Salt Water; this Mint became perfectly dead within three Days.

Another Mint I put into a Glass of fair Water; but I immers’d 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 dy’d also very soon.

Of another (standing in a Glass of Water and Earth till it grew vigorously) I ty’d one single Root into a Bag, which held a Spoonful of dry Salt, adjoining to the Top of the Glass, which kill’d this strong Mint also. I found that this Salt was soon dissolv’d, tho’ on the Outside of the Glass; and tho’ no Water reach’d so high, as to be within Two Inches of the Joint which produc’d this Root: The Leaves of all these were salt as Brine to the Taste.

Of another, I put an upper Root into a small Glass of Ink, instead of a Bag of Salt, in the Manner above-mention’d; this Plant was also kill’d by some of the Ink Ingredients. The Blackness was not communicated to the Stalk, or Leaves, which inclin’d rather to a yellowish Colour as they died, which seem’d owing to the Copperas.

I made a very strong Liquor with Water, and bruised Seeds of Wild-Garlick, and, filling a Glass therewith, plac’d the Top of it close to the Top of another Glass, having in it a Mint, two or three of whose upper Roots, put into this stinking Liquor, full of the bruised Seeds, and there remaining, it kill’d the Mint in some time; but it was much longer in dying than the others were with Salt and Ink. It might be, because these Roots in the Garlick 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 poison’d, did to theirs.

When the Edges of the Leaves began to change Colour, I chew’d many of them in my Mouth, and found at first the strong aromatic Flavour of Mint, but that was soon over; and then the nauseous Taste of Garlick was very perceptible to my Palate.

I observ’d, that when the Mint had stood in a Glass of Water, until it seem’d to have finish’d 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 reach’d the Earth at the Bottom; and then, after some time, came to be of the same earthy Colour with the old ones.

Another Mint being well rooted from Two Joints, about Four Inches asunder; I plac’d the Roots of the lower Joint in a deep Mint-Glass, having Water at the Bottom, and the Roots of the upper Joint into a square Box, contriv’d for the Purpose, standing over the Glass, and having a Bottom, that open’d 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 fill’d it with Sand, dry’d in a Fire-shovel, and found, that in one Night’s time, the Roots of the lower Joint, which reach’d 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 Corner 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 prepar’d a small Trough, about two Foot long, and plac’d a Mint-Glass under each End of the Trough; over each Glass I plac’d 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 cover’d these Roots with pulveriz’d Earth, and kept the Glasses supply’d with Water; and as oft as the white fibrous Roots shot thro’ the Earth, I threw on more Earth, till the Trough would hold no more; and still the white Fibres came thro’, and appear’d above it; but all seem’d (as I saw by the Help of a coarse Microscope) to turn, and when they came above-ground, their Ends enter’d into it again. These two Mints grew thrice as large as any other Mint 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. Tho’ these two, standing in my Chamber, never had any Water in their Earth, but what those Roots, which reach’d 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 Troughs moist, tho’ of a thousand times greater Quantity than the Roots which water’d it, makes it probable, that the Water pass’d out of the Roots into the Earth, without mixing at all with the Sap, or being alter’d to any Degree. The Earth kept always moist, and in the hot Weather there would not remain a Drop of Water in the Glasses, when they had not been fresh supply’d in two Days and one Night; and yet these Roots in the Glasses were not dry’d, tho’ they stood sometimes a whole Day and Night thus in the empty Glasses. These two Mints have thus liv’d all one Summer.

Remarks on the Mints, &c.

Tho’ the Vessels of Marine Plants be some ways fortify’d against the Acrimony of Salt, as Sea-fish are, yet the Mints all shew, 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 try’d Salt to many Potatoes in the Ground being undermin’d, and a few of their Roots put into a Dish of Salt-water, they all died sooner or later, according to their Bigness, and to the Proportions the Quantity of Salt apply’d did bear to them.

By the Mints 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, Garlick, and Ink offer’d to them.

The sixth Mint shews, that when new Earth is apply’d 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 form’d, by the new Vigour the Plant takes from the Addition of Earth. This corresponds with the Action of Hoing; for every time the Earth is mov’d about Roots, they have a Change of Earth, which is new to them.

The seventh Mint 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; tho’ the clear Stalk (through which it must have pass’d) that was betwixt these two Joints, was several Inches in Length.

This accounts for the great Produce of long tap-rooted Plants, such as Lusern 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 retain’d 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 ’tis certain, that if this dry Surface be mov’d or dung’d, the Plant will be found to grow the faster, tho’ no Rain falls; 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 the Mints they did.

The two last Mints shew, 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 these could not have continu’d plump and fresh, as they did for 24 Hours in the empty Glass. And I have since observed them to do so, in the cooler Season of the Year, for several Weeks together, without any other Water, than what the upper Roots convey’d to them, from the moist Earth above in the Trough[4]. I know not what Time these Roots might continue to be supply’d thus in the hot Weather, because I did not try any longer, for fear of killing them.

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 dry’d them, if they had been out of the Glass.

In this Trough is shewn most of the Hoing 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 stirr’d about them.

That the stirring the Earth makes the Plants grow the faster.

Leaves are the Parts or Bowels of a Plant, which perform the same Office to Sap, as the Lungs of an Animal do to Blood; that is, they purify or cleanse it of the Recrements, or fuliginous Steams, received in the Circulation, being the unfit Parts of the Food; and perhaps some decay’d Particles, which fly off the Vessels, through which Blood and Sap do pass respectively.

Besides which Use, the Nitro-aerous Particles may there enter, to keep up the vital Ferment or Flame.

Mr. Papin shews, that Air will pass in at the Leaves, and out thro’ the Plant at the Roots, but Water will not pass in at the Leaves; and that if the Leaves have no Air, a Plant will die; but if the Leaves have Air, tho’ the Root remain in Water in vacuo, the Plant will live and grow.

Dr. Grew, in his Anatomy of Plants, mentions Vessels, which he calls, Net-work, Cobweb, Skeins of Silk, &c. but above all, the Multitude of Air-Bladders in them, which I take to be of the same Use in Leaves, as the Vesiculæ are in Lungs. Leaves being as Lungs inverted, and of a broad and thin Form; their Vesiculæ are in Contact with the free open Air, and therefore have no need of Trachea, or Bronchia, nor of Respiration.