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Jethro Tull Guest Writes on Roots and Circulatory Systems of Plants

We’re taking the day off from writing blogs - and are glad to present to you today Jethro Tull, in his very first blog. Though he died in 1731, by this active and energetic assay into the blogosphere, he seems just as innovative as when he perfected the seed drill in 1701, doesn’t he? Fairly spry for a dead guy…

Seriously, this is an excerpt from his amazing, ground-breaking (forgive the pun) book on agriculture, “the Horse Hoeing Husbandry.” It was supposed to have been named “the Deep Hoeing Husbandry” but his publisher got creative and didn’t tell him. It improves (partially) on Columella’s “Agriculture,” and brought the scientific revolution to bear upon the art of crop production.

We have updated his book with modern science, and completed Mr. Tull’s work of improving upon Columella’s “Agriculture,” and will be publishing it this year. This, as all our books, will be available for free online download ( We’ve got a lot of good books for free - for you.

But without further delay, here is Mr. Tull himself, now speaking fully modernized American English, on the subject of determining the distance from the plant that roots extend, and on his amazing experiments with mint, demonstrating a circulatory system.

1. The Distance to which Roots Extend Horizontally

By this method the distance of the extent of the roots of any plant may be discovered. Dig a piece or plot and make fine in whole hard ground, the smaller end (A) two feet and the wider end (B) twelve feet. The length of the piece should be 60 feet. Plant twenty turnips (labeled “1” through “20”) at equal spacing. Hoe as closely as possible to the first plants with a spade and with each successive plant, hoe a foot further distance—six inches to each side. Make sure to dig deep each time, so that it will be the finer for the roots to enter when they are permitted to grow that distance.

If these turnips are all gradually bigger as they stand nearer to the end B, it is a proof that their roots extend so far from their center: if the turnip 20 is biggest, it is because it draws nourishment from all the land six feet from its center; but if turnips 16, 17, 18, 19, and 20 acquire no greater bulk than the turnip 15, it is clear that the roots of the turnips extend no farther than those of turnip 15 do (about four feet).

There is another way to find the length of roots. Make a long narrow trench at the distance you expect the roots to extend and fill it with salt. If the plant is killed by the salt, it is certain that at least some of the roots entered into it.

What put me on to this method was an observation of two lands drilled with turnips in rows, a foot apart, at very even intervals. At both ends and one side was hard and unplowed soil. The turnips were not hoed and were very poor, small and yellow—except for the three outside rows (B, C and D) which stood next to the hoed soil (E). The soil E was hoed and harrowed at the time the soil A ought to have been and gave to the three outside rows (B, C and D) a very dark flourishing color. The turnips received so much benefit from it as to grow twice as big as any of the more distant rows. The second-nearest row C, being a foot nearer to the new plowed land, became twice as large as those in the further row D, but the middle row B, which was even nearer to the plowed land, grew much larger yet.

The land of hard unbroken ground (F) was about two perches in length and about two to three feet across. It is remarkable that for the length of this interadjacent hard ground F, the rows B, C and D were as small and yellow as any in the land E. That the turnips in row D, about one foot distance from land E received a double increase proves that they had as much nourishment from the land E as from the land A on which they were planted. In their own land (A) their roots must have extended at least three feet or else they could not have reached the land E.

In pulling up the aforementioned turnips, their roots seemed to end at a few inches distance from the plants, but one cause of peoples’ not suspecting roots to extend even to the twentieth part of the distance they actually do is from observing these horizontal roots near the plant to be pretty taper and assuming that if they continued to diminish at the rate they had until that point, they must soon come to an end. But the truth is that, after a few inches, the roots do not discernibly taper and pass to their ends very near the same bigness. This may be seen by experiment in growing roots in water.
Upon pulling up a carrot, I found an extremely small fiber on its side. It was much less wide than a hair, but through a microscope it appeared quite large. It was not taper, but broken off short at its end. It is probable that it never extended near as far as the turnip roots did. It had many fibers going 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. These fine roots, as demonstrated by the land F, cannot penetrate soil unless the soil is broken open by tillage.
All roots—of trees and other plants—follow open soil. Roots can descend perpendicularly and mount again the same manner. In an orchard where the trees are planted too deep below the staple, the roots (at even a little distance from the stem) are all as near to the upper superficies as those trees that are planted higher than the soil’s surface. The damage of planting a tree too low in moist ground is that in passing through this low part the sap is chilled and its circulation is thereby retarded—not an inaccessibility to the staple.

I have observed the roots of a hedge to do this when passing a steep ditch two feet deep to reach the soil on the other side. When I dug five feet from the ditch, I found the roots there large—though this soil was very shallow and there were no roots below the good, open soil.

And I have seen a chalk pit (contiguous with a barn) the area of which was about forty perches of ground, was made clean and swept so that there was not the appearance of any part of a vegetable. Straw was thrown from the barn into the pit for cattle to lie on. The dung made thereby was carried away about three years after the pit had been cleaned when, at the bottom of it and on top of the chalk, the pit was covered all over with roots that came from a witch-elm that stood five yards above and six yards in length away from the pit. The witch-elm itself was only five yards tall, but in three years the roots grew themselves eight times the length of the tree beyond the extremities of the old roots. The annual increased length of the roots was three times as much as the height of the tree. I have seen this too in wheat: wheat, drilled, in double rows in November, in a field well tilled before planting, looked yellow when eighteen inches high. At two feet distance from the plants the soil was plowed. This gave such nourishment to the wheat that they recovered their health and changed their sickly yellow to a lively green.

2. Experiments with Mint
I. Experiments with Mints

That the color of the roots are different from the color of the leaves and other external parts of a plant is no argument against the circulation of the sap than to argue against a circulation of the blood by saying, “the color of the guts is different from that of the lungs and other parts of the animal body.” As far as I can discover, all roots (if they are properly described) are white. Even the red carrot sends out in the spring from all parts of it many fibrous roots, all as white as those of any other plant. The white color of roots comes from the vessels that circulate the chyle to the other parts of the plant.

When a good number of mint stalks had stood in water until they were well stocked with roots from their two lower joints (some of them from the three lowest joints) I set one into a glass (marked “A”) full of salt water. This mint A was 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 another glass) into another glass of salt water. This mint also died very soon .

Another mint (marked “C”) stood in a glass of water and soil until it grew vigorously. I put one single root into a bag containing a spoonful of dry salt. Besides finding that this mint died also, I found that this salt was dissolved in water as high as the second joint of the root that was placed into it, and that the leaves of the mint tasted of salt.

I put a single root of another mint (marked “D”) into a small glass of ink as I had done when I put a root of mint C into a bag of salt. This plant was killed by some of the ink ingredients, but the blackness was not communicated to the stalk or leaves (which instead inclined to rather a yellowish color when they died, which seemed owing to the copperas in the ink).

For another mint (marked “E”), I made a very strong solution of water and the bruised seeds of wild garlic. I placed a couple of roots into this stinking liquor. This solution killed the mint after some time, but it was much longer in dying than the others were when exposed to salt and ink. This slower death may be because these roots in the garlic were 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 of mint E began to change color, I chewed some of them in my mouth and found at first the strong aromatic flavor of mint. But that taste was soon replaced by the nauseous taste of garlic, which was very perceptible to my palate.

I have observed with another mint (marked “F”) that when mint has stood in a glass of water until it seemed to have finished its growth, the roots are a foot long and of an earthy color. When I put some fine soil into the water, it sunk to the bottom and soon there came from the upper joint a new set of white roots. These new white roots took their course on the outside of the heap of old roots downwards until they reached the earth at the bottom. Then they came to be of the same earthy color as the old ones.

Another mint (marked “G”), was well rooted from two joints about four inches apart. I put the roots of the lower joint in a deep glass of water and the roots of the upper joint into a square box of sand, which I had contrived for the purpose of standing over the glass of water: the box had a hole in it through which the mint stood, allowing the roots of the upper joint to be laid easily into one corner of the box of sand. The sand I filled the box with was first dried in a fire, but within only one night’s time I found that the roots of the lower joint had drawn the water up and imparted so much of the water to the dry sand above that the sand that the corner in which the roots of the upper joint lay was very wet (the other three corners were dry). This experiment I repeated very often and it always succeeded as it did the first time.

I prepared in my chamber a small trough (about two feet long) and placed a mint growing in a glass of water at each end of the trough (both marked “HH”). Half of the roots of each mint were allowed to stay in the water, the other half placed into the ends of the trough. I then covered the roots in the trough with loose soil and kept the glasses supplied with water. Whenever the roots would grow through the loose soil, I would put more on until the trough would hold no more. And still the white fibrous roots grew through the dirt, appearing above it. With a microscope I saw that these roots, upon coming above the ground, entered their ends into it again.

These two mints (HH) in my chamber grew three times as large as any other mint I had that stood in glasses of water (which were many!) and much larger than those which stood in water with earth in it (those being of an equal bigness when they were set in)—even though these two mints never had any water in their earth but what their roots sent up from the glasses. There was such a vast quantity of water these roots sent up that it was sufficient to keep all the earth in the troughs moist, though there was a thousand times greater quantity of soil than the roots that watered it. It is probable that the water passed out of the roots into the earth without mixing at all with the sap or being altered in any degree . The earth was always kept moist and even while in the hot weather there would not remain even a drop of water in the glasses after two days and a night, the roots in the glasses were never dry.

Demonstrating a Circulation from the Roots of Sap and Chyle
II. Remarks on the Mints

Though some marine plants are in some ways fortified against the acrimony of salt, the mints A, B and C each demonstrate that salt is poison to other plants. The reason why salts in dung, brine or urine do not kill plants in the field or garden is that their strength is diffused in the soil so that the no considerable quantity or force of the salts reaches the roots.

I tried applying salt to many potatoes growing in the ground. I undermined them and put a few of their roots into a dish of salt water. These roots all died sooner or later (according to their bigness). By these potatoes and the mints B, C, D and E, it appears that roots make no distinction between nourishment and poison. And, they are not brought to ingesting poison for lack of nourishment—they were vigorous and well fed at the time when the most inconsiderable part of their number was exposed to salt, garlic or ink.

The mint F shows that when new soil is applied to old roots, a plant sends out new roots for the purpose of feeding upon the new soil. The more earth that is given, the more roots will be formed and the greater the vigor of the plant. This addition of soil corresponds with the action of hoeing: every time the soil is moved about the roots, it is as if they have a change of soil (though it is true the soil is not new, the soil that has been moved is new to them).

The mint G proves that there is such a communication between the roots so that when any of them have water, they share of that water with the rest. This also demonstrates that the root of the lower joint of the mint had passages (or “vessels”) leading from them (through the stalk) to the roots of the upper joint.

The circulation of sap and chyle accounts for the great produce of the plants with long tap-roots, such as alfalfa and sanfoin in dry weather: the soil at great depths is always moist, even if the soil at shallow depths may be dry. It accounts for the good crops of these plants we have in dry summers upon land that has a clay bottom, for in that clay bottom the water is retained a long time and the lower roots of the plants that reach it do like those of the mint G and send up a share of that water to all the higher roots. If those roots of a plant that lie at the surface of the ground did not receive moisture from other roots that lie deeper, they could be of no use in dry weather and when the dry surface is loosened or fertilized, the plant would not grow faster if no rain fell. The deep roots communicate a share of the water to the shallow roots and in return the shallow roots send a share of the food: the two mints, marked HH show that when the upper roots have moisture (as they had in the earth in the trough, carried there by the lower roots), they impart some of it to the lower when the lower roots require water.

These mints demonstrate the circulation of sap and chyle and explain the benefit of the hoeing effects: loosening the soil encourages the plants to grow. Roots, by being broken off near their ends, increase their number and send out several where one is broken off, and roots increase their fibers every time the soil is loosened about them.

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