Of PASTURE OF PLANTS.
The pasture of cattle has been known and understood in all ages of the world, it being liable to inspection ; but the pasture of plants, being out of the observations of the senses, is only to be known by disquisitions of reason, and has (for aught I can find) passed undiscovered by the writers of husbandry*.
The ignorance of this seems to be one principal cause, that agriculture, the most necessary of all arts, has been treated of by authors more superficially than any other art whatever.
The food, or pabulum, of plants being proved to be earth, where and whence** they take that, may properly be called their pasture.
This pasture I shall endeavor to describe.
* When writers of husbandry, in discoursing of earth and vegetation, come nearest to the thing, that is, the pasture of plants, they are lost in the shadow of it, and wander in a wilderness of obscure expressions, such as magnetism, virtue, power, specific quality, certain quality, and the like, wherein there is no manner of light for discovering the real substance ; but we are left by them more in the dark to find it, than roots are when they feed on it. And when a man, no less sagacious than Mr. Evelyn, has traced it through all the mazes of the occult qualities, and even up to the metaphysics, he declares he cannot determine whether the thing he pursues be corporeal or spiritual.
** By the pasture is not meant the pabulum itself, but the superficies from whence the pabulum in taken by roots.
It is the inner (or internal) superficies* of the earth ; or, which is the same thing, it is the superficies of the pores, cavities, or interstices of the divided parts of the earth, which are of two sorts, viz., natural and artificial.
By nature, the whole earth (or soil) is composed of parts ; and if these had been in every place absolutely joined, it would have been without interstices, or pores, and would have had no internal superficies, or pasture for plants ; but, since it is not so strictly dense**, there must be interstices at all those places where the parts remain separate and divided.
These interstices, by their number and largeness, determine the specific gravity (or true quantity) of every soil, the larger they are, the lighter is the soil ; and the inner superficies is commonly the less.
The mouths, or lacteals, being situate, and opening in the convex superficies of roots, they take their pabulum, being fine particles of earth, from the superficies of the pores, or cavities, wherein the roots are included.
* This pasture of plants never having been mentioned or described by any author that I know of, I am at a loss to find any other term to describe it by, that may be synonymous, or equipollent to it ; therefore, for want of a better, I call it the inner, or internal superficies of the earth, to distinguish it from the outer, or external superficies, or surface whereon we tread. Inner or internal superficies, may be thought an absurd expression, the adjective expressing something within, and the substantive seeming to express only what is without it, and indeed, the sense of the expression is so ; for the vegetable pasture is within the earth, but without (or on the outsides) the divided parts of the earth. And besides, superficies must be joined with the adjective inner (or internal) when it is used to describe the inside of a thing that is hollow, as the pores and interstices of the earth are. The superficies, which is the pasture of plants, is not a bare mathematical superficies, for that is only imaginary.
** For were the soil as dense as glass, the roots, or vegetables (such as our earth produces) would never be able to enter its pores.
And it is certain, that the earth is not divested or robbed of this pabulum, by any other means than by actual fire, or the roots of plants.
For when no vegetables are suffered to grow in a soil, it will always grow richer. Plough it, harrow it, as often as you please ; expose it to the sun in horse-paths all the summer, and to the frost of the winter ; let it be covered by water at the bottom of ponds or ditches, or if you grind dry earth to powder, the longer it is kept exposed, or treated by these or any other method possible (except actual burning by fire), instead of losing, it will gain the more fertility.
These particles, which are the pabulum of plants, are so very minute* and light, as not be singly attracted to the earth, if separated from those parts to which they adhere**, or with which they are in contact (like dust to a looking-glass, turn it upwards, or downwards, it will remain affixed to it), as these particles do to those parts, until from thence removed by some agent. A plant cannot separate these particles from the parts to which they adhere, without the assistance of water, which helps to loosen them.
* As to the fineness of pabulum of plants, it is not unlikely that roots may insume no grosser particles than those on which the colours of bodies depend ; but to discover the greatness of those corpuscles, Sir Isaac Newton thinks, will require a microscope that with sufficient distinctness can represent objects five or six hundred times bigger than at a foot distance they appear to the naked eye. My microscope indeed is but a very ordinary one, and when I view with the liquor newly imbibed by a fibrous root of a mint, it seems more limpid than the clearest common water, nothing at all appearing in it.
** Either roots must insume the earth, that is, their pabulum, as the find it in whole pieces, having entire superficies of their own, or else such particles as have not entire superficies of their own, but want some part of it, which adheres to, or is part of the superficies of larger particles, before they are separated by roots. The former they cannot insume (unless contained in water), because they would fly away at the first pores that were open : ergo, they must insume the latter.
And it is also probable, that the nitre of the air may be necessary to relax this superficies, to render the prolific particles capable of being thence disjoined ; and this action of the nitre seems to be what is called impregnating the earth.
Since the grosser vegetable particles, when they have passed through a plant, together with their moist vehicle, do fly up into the air invisibly, it is not likely they should, in the earth, fall off from the superficies of the pores by their own gravity ; and if they did fall off, they might fly away as easily before they entered plants as they do after they have passed through them ; and then a soil might become the poorer*, for all the culture and stirring we bestow upon it, though no plants were in it, contrary to experience.
It must be owned, that water does every carry in its interstices particles of earth, fine enough to enter roots ; because I have seen, that a great quantity of water (in my experiments) will pass out of roots set in rain-water ; and it is found that water can never be, by any art, wholly freed from its earthy charge ; therefore it must have carried in some particles of earth along with it ; but yet, I cannot hence conclude, that the water did first take these fine particles from the aforesaid superficies. I rather think that they are exhaled, together with very small pieces to which they adhere, and in the vapour divided by the aerial nitre, and when the vapour is condensed, they descend with it to replenish the pasture of plants ; and that these do not enter entire into roots, neither does any other of the earthy charge that any water contains ; except such fine particles which have already passed through the vegetable vessels, and been thence exhaled.
* But we see it is always the richer by being frequently turned and exposed to the atmosphere : therefore plants must take all their pabulum from a superficies of parts of earth ; except what may perhaps be contained in water fine enough to enter roots entire with the water.
This conjecture is the more probable, for that rain-water is as nourishing to plants set therein, as spring-water, though the latter have more earth in it ; and though spring-water have some particles in it, that will enter entire into roots, yet we must consider, that even that water may have been many times exhaled into the air, and may have still retained a great quantity of vegetable particles, which it received from vegetable exhalations in the atmosphere, though not so great a quantity as rain-water, that comes immediately thence.
These, I have to do with, are the particles which plants have from the earth, or soil ; but they have also fine particles of earth from water, which may impart some of its finest charge to the superficies of roots, as well as to the superficies of the parts of the earth*, which makes the pasture of plants.
Yet is seems, that much of the earth contained in the clearest water is there in too large parts to enter a root ; since we see that in a short time the root's superficies will in the purest water be covered with earth, which is then formed into a terrene pasture, which may nourish roots ; but very few plants will live long is so thin a pasture as any water affords them. I cannot find one, as yet, that has lived a year without some earth having been added to it.
And all aquatics, that I know, have their roots in the earth, though covered with water.
The pores, cavities, or interstices of the earth, being of two sorts, viz., natural and artificial ; the one affords the natural, the other the artificial pasture of plants.
The natural pasture alone will suffice to furnish a country with vegetables for the maintenance of a few inhabitants, but if agriculture were taken out of the world, it is much to be feared, that
* If water does separate, and take any of the mere pabulum of plants from the soil, it gives much more to it.
those of all populous countries, especially towards the confines of the frigid zones (for there the trees often fail of producing fruit), would be obliged to turn anthropophagi, as in many uncultivated regions they do, very probably for that reason.
The artificial pasture of plants is that inner superficies which is made from dividing the soil by art. This does, on all parts of the globe where used, maintain many more people than the natural pasture* ; and in the colder climates, the natural pasture is not only less than the artificial, in an equal quantity of earth, but also that little consisting in the superficies of pores, or cavities, not having a free communication** with one another, are less pervious to the roots of all vegetables, and which require a greater force to break through their partitions ; by that means roots, especially of weak plants, are excluded from many of those cavities, and so lose the benefit of them.
* The extraordinary increase of St-Foin, clover, and natural grass, when their roots reach into pulverised earth, exceeding the increase of all those other plants of the same species (that stand out of the reach of it), above one hundred times, show how vastly the artificial pasture of plants exceeds the natural. A full proof of this difference (besides very many I have had before), was seen by two intervals in the middle of a poor field of worn out St.-Foin, pulverised in the precedent summer, in the manner described in p. 8. Here not only the St.-Foin adjoining to these intervals recovered its strength, blossomed, and seeded well, but also the natural grass amongst it was as strong, and had as flourishing a colour, as if a dung-heap had been laid in the intervals : also many other weeds came out from the edges of the unploughed ground, which must have lain dormant a great many years, grew higher and larger than ever were seen before in that field ; but above all, there was a weed amongst the St.-Foin, which generally accompanies it, bearing a white flower ; some call it white-weed, others, ladies'-bedstraw. Some plants of this that stood near the intervals, were, in the opinion of all that saw them, increased to a thousand times the bulk of those of the same species, that stood in the field three feet distant from such pulverised earth.
** None of the natural vegetable pasture is lost or injured by the artificial, but, on the contrary, it is mended by being mixed with it, and by having a greater communication betwixt pore and pore.
But the artificial pasture consists in superficies of cavities, that are pervious to all manner of roots, and that afford therm free passage and entertainment in and through all their recesses. Roots may here extend to the utmost without meeting with any barricadoes in their way.
The internal superficies, which is the natural pasture of plants, is like the external superficies, or surface of the earth, whereon is the pasture of cattle ; in that it cannot be enlarged without addition of more surface taken from land adjoining to it by enlarging its bounds or limits.
But the artificial pasture of plants may be enlarged wihout any addition of land, or enlarging of bounds, and this by division only of the same earth.
Note. These intervals were each an hundred perch long, and had each in them a treble row of barley, very good. The reason I take to be this, that the land having lain still several years after its artificial pasture was lost, whereby all the plants in it having only the natural pasture to subsist on, became so extremely small and weak, that they were not able to exhaust the land of so great a quantity of the (vegetable) nourishing particles as the atmospheres brought down to it. And when by pulverisation the artificial pasture came to be added to this natural pasture, not much exhausted, and nothing at all suffered to grow out of it for above three-quarters of a year, it became rich enough, without any manure, to produce this extraordinary effect upon the vegetables, whose roots reached onto it. How long this effect may continue is uncertain ; but I may venture to say, it will continue until the exhaustion by vegetables doth overbalance the descent of the atmosphere and the pulverisation. And what I have said of any one species of plants in this respect may be generally applied to the rest. I believe it will not be extravagant to say, ten times as many : or, that in case agriculture were a little improved (as I hope to show is not difficult to be done), it might maintain twice as many more yet, or the same number better.
And this artificial pasture many be increased in proportion to the division of the parts of earth, whereof it is the superficies, which division may be mathematically infinite ; for an atom is nothing ; neither is there a more plain impossiblility in nature, than to reduce matter to nothing by division or separation of its parts.
A cube of earth of one foot has but six feet of superficies. Divide this cube into cubical inches, and then its superficies will be increased twelve times, viz., to seventy-two superficial feet. Divide these again in like manner and proportion ; that is, divide them into parts that bear the same proportion to the inches as the inches do to the foot ; and then the same earth, which had at first no more that six superficial feet, will have eight hundred sixty-four superficial feet of artificial pasture, and so is the soil divisible, and this pasture increasible, ad infinitum.
Poor land does not afford an internal superficies so well stocked with these fruitful particles, as rich land does, but this we may compensate by dividing it more ; to the end that what this artificial pasture wants in quality, may, by division, be made up in quantity.
The common methods of dividing the soil are these, viz., by dung, by tillage, or by both*.