Of FOOD OF PLANTS.
It is agreed that all the following materials contribute in some manner to the increase of plants, but it is disputed which of them is that very increase or food. 1 . Nitre. 2. Water. 3. Air. 4. Fire. 5. Earth.
I will not mention, as a food, that acid spirit of the air, so much talked of ; since, by its eating asunder iron bars, it appears too much of the nature of aqua-fortis to be a welcome guest alone to the tender vessels of the roots of plants.
Nitre is useful to divide and prepare the food, and may be said to nourish vegetables in much the same manner as my knife nourishes me, by cutting and dividing my meat ; but when nitre is applied to the root of a plant, it will kill as certainly as a knife misapplied will kill a man : which proves that nitre is, in respect of nourishment, just as much the food of plants, as white arsenic is the food of rats. And the same may be said of salts.
Water, from Van Helmont's experiment, was by some great philosophers thought to be it. But these were deceived, in not observing that water has always in its intervals a charge of earth, from which no art can free it. This hypothesis having been fully confuted by Dr. Woodward, nobody has, that I know of, maintained it since : and to the Doctor's arguments I shall add more in the article of air.
Air, because its spring, &c. is as necessary to the life of vegetables as the vehicle of water is, some modern virtuosi have affirmed, from the same and worse arguments than those of the water-philosophers, that air is the food of plants. Mr. Bradley being the chief, if not only author, who has published this fantasie, which at present seems to get ground, it is fit he should be answered, and this will be easily done, if I can show, that he has answered this his own opinion by some or all of his own arguments.
His first is, that of Helmont, and is thus related in Mr. Bradley's General Treatise of Husbandry and Gardening, vol i. p. 36, " Who dried two hundred pounds of earth, and planted a willow of five pounds weight in it, which he watered with rain, or distilled water ; and to secure it from any other earth getting in, he covered it with a perforated tin cover. Five years after, weighing the tree, with all the leaves it had borne in that time, he found it to weigh one hundred sixty-nine pounds three ounces ; but the earth was only diminished about 2 ounces in the weight. "
On this experiment Mr. Bradley grounds his airy hypothesis. But let it be but examined fairly, and see what may be thence inferred.
The tin cover was to prevent any other earth from getting in. This must also prevent any earth from getting out, except what entered the roots, and by them passed into the tree.
A willow is a very thirsty tree, and must have drank in five years time several tuns of water ; which must necessarily carry in its interstices a great quantity of earth (probably many times more than the tree's weight*) which could not get out, but by the roots, of the willow.
Therefore the two hundred pounds of earth not being increased, proves, that so much earth as was poured in with the water did enter the tree.
* The body of an animal receives a much less increase in weight than its perspirations amounts to, as Sanctorius's Static Chair demonstrates.
Whether the earth did enter to nourish the tree, or whether only in order to pass through it (by way of vehicle to the air) and leave the air behind for the augmentation of the willow, may appear by examining the matter of which the tree did consist.
If the matter remaining after the corruption or putrefaction of the tree be earth will it not be a proof, that the earth remained in it to nourish and augment it ? for it could not leave what it did not first take, nor be augmented by what passed through it. According to Aristotle's doctrine, and Br. Bradley's too, in Vol. I. p. 72, " Putrefaction resolves it again into the earth, its first principle."
The weight of the tree, even when green, must consist of earth and water. Air could be no part of it, because air being of no greater specific gravity than the incumbent atmosphere, could not be of any weight in it ; therefore was no part of the one hundred sixty-nine pounds three ounces.
Nature has directed animals and vegetables to seek what is most necessary to them.
At the time when the foetus has a necessity of respiration it is brought forth into the open air, and then the lungs are filled with air. As soon as a calf, lamb, &c. is able to stand, it applies to the teat for food, without any teaching. In like manner Mr. Bradley remarks, in his Vol. I. p. 10, " That almost every stem and every root are formed in a bending manner under ground, and yet all these stems become straight and upright when they come above ground, and meet the air ; and most roots run as directly downwards, and shun the air as much as possible."
Can any thing more plainly show the intent of nature, than this his remark, does, viz. That the air is most necessary to the tree above the ground, to purify the sap by the leaves, as the blood of animals is depurated by their lungs ? And that roots seek the earth for their food, and shun the air, which would dry up and destroy them ?
No one truth can possibly contradict or interfere with any other truth ; but one error may contradict and interfere with another error, viz.
Mr. Bradley and all authors, I think, are of opinion, that plants of different natures are fed by a different sort of nourishment ; from whence they aver, that a crop of wheat takes up all that is peculiar to that grain ; then a crop of barley all that is proper to it ; next a crop of peas, and so on, until each has drawn off all those particles which are proper to it ; and then no more of these grains will grow in that land, until by fallow, dung and influences of the heavens, the earth will be again replenished with new nourishment, to supply the same sorts of corn over again. This, if true (as they all affirm it to be), would prove that the air is not the food of vegetables. For the air being in itself so homogeneous as it is, could never afford such different matter as they imagine, neither is it probable that the air could afford the wheat nourishment more one year than the ensuing year. Or that the same year it should nourish barley in one field, wheat in another, peas in a third ; but that if barley were sown in the third, wheat in the first, peas in the second, all would fail. Therefore this hypothesis of air for food interferes with and contradicts this doctrine of necessity of changing sorts.
I suppose, by air, they do not mean dry particles of earth, and the effluvia which float in the air, the quantity of these is too small to augment vegetables to that bulk they arrive at. By that way of speaking they might more truly affirm this of water because it must be like to carry a greater quantity of earth than air doth, in proportion to the difference of their different specific weights ; water being about 800 times heavier than air, is likely to have 800 times more of that terrestrial matter in it; and we see this is sufficient to maintain some sorts of vegetables, as aquatics. But
the air, by its change of effluvia, &c., is never able to maintain or nourish andy plant ; for as to the sedums, aloes, and all others that are supposed to grow suspended in the air, it is a mere fallacy ; they seem to grow, but do not ; since they constantly grow lighter, and though their vessels may be somewhat distended, by the ferment of their own juices, which they received in the earth, yet, suspended in the air, they continually diminish in weight (which is the true increase of a plant) until they grow to nothing. So that this instance of sedums, &c. which they pretend to bring for proof of this their hypothesis, is alone a full confutation of it.
Yet if granted, that air would nourish some vegetables by the earthy effluvia, &c., which it carried with it*, even that would be against them, not for them.
They might as well believe that martins and swallows are nourished by the air because they live on flies and gnats, which they catch therein ; this being the same food which is found in the stomach of the cameleon.
If as they say, the earth is of little other use to plants but to keep them fixed and steady, there would be little or no difference in the value of rich and poor land, dunged or undunged ; for one would serve to keep plants fixed and steady very near, if not quite, as well as the other.
If water or air were the food of plants, I cannot see what necessity there should be of dung or tillage.
4. Fire. No plant can live without heat, though different degrees of it be necessary to different sorts of plants. Some are almost able to keep company with the salamander, and do live in the hottest
* This is meant of dry earth, by its lightness (when pulverized extremely fine) carried in the air without vapour : for the atmosphere, consisting of all the elements, has earth in considerable quantity, mixed with water ; but a very little earth is so minutely divided, as to fly therein pure from water ; which is its vehicle there for the most part.
exposures of the hot countries. Others have their abode with fishes, under water, in cold climates ; for the sun has his influence, though weaker, upon the earth covered with water, at a considerable depth, which appears by the effect the vicissitudes of winter and summer have upon the subterraqueous vegetables.
But that fire is the food of plants, I do not know any author has affirmed, except Mr. Lawrence ; who says, " They are true fire-eaters." And even he does not seem to intend, that this expression of his should be taken literally ; yet, if he had meant it in the plain sense the words import, perhaps he might have been much nearer the truth than Mr. Bradley with his air. For if fire be nothing else but the minutest parts of terrestrial matter, put into a violent motion, then those minute parts out of that motion are the same matter as when in it ; and these being the true nourishment of plants, that and fire differ in nothing but the motion.
Fire is a fluid sui generis ; but that it pervades all bodies, and there remains latent ; if excited by violence is hot ; if at rest may be cold, being against the essential property of fire : that notion cannot pervade the skull of a peasant to make him believe fire can ever be cold.
But if we define fire to be the action of burning, not the matter which burns, then fire will be as different from the food of plants as the air is.
Indeed the true food of plants may be also the fuel of fire, which is so greedy of that food as to carry it all away that comes within reach of the flames ; and I know no way by which the earth can be divested of its vegetative particles, but by actual fire, or the roots of plants.
Though every heat is said to be a different degree of fire, yet we may distinguish the degrees by their different effects. Heat warms, but fire burns ; the first helps to cherish, the later destroys, plants.
5. Earth. That which nourishes and augments a plant, is the true food of it.
Every plant is earth, and the growth and true increase of a plant is the addition of more earth.
Nitre (or other salts) prepares the earth, water and air move it, by conveying and fermenting it in the juices, and this motion is called heat.
When this additional earth is assimilated to the plant, it becomes an absolute part of it.
Suppose water, air, and heat, could be taken away, would it not remain to be a plant, though a dead one ?
But suppose the earth of it taken away, what would then become of the plant ? Mr. Bradley might look long enough after it, before he found it in the air amidst his specific or certain qualities.
Besides, too much nitre (or other salts) corrodes a plant ; too much water drowns it ; too much air dries the roots of it ; too much heat (or fire) burns it ; but too much earth, a plant never can have, unless it be therein wholly buried ; and in that case it would be equally misapplied to the body, as air or nitre would be to the roots.
Too much earth, or too fine, can never possibly be given to roots ; for they never receive so much of it as to surfeit the plant, unless it be deprived of leaves, which as lungs, should purify it.
And earth is so surely the food of all plants, that with the proper share of the other elements, which each species of plants requires, I do not find but that any common earth will nourish any plant.
The only difference of soil (except the richness) seems to be the different heat and moisture it has ; for if those be rightly adjusted, any soil will nourish any sort of plant. For let thyme and rushes change places, and both will die ; but let them change their soil, by removing the earth wherein the thyme grew, from the dry hill down to the watery bottom, and plant rushes therein ; and carry the moist
earth, wherein the rushes grew, up to the hill ; and there thyme will grow in the earth, that was taken from the rushes ; and so will the rushes grow in the earth that was taken from the thyme ; so that it is only more or less water that makes the same earth fit either for the growth of thyme or rushes.
As I have said in my Essay, that a soil being once proper to a species of vegetables, it will always continue to be so. It must be supposed that there be no alteration of the heat and moisture of it ; and that this difference, I mean, is of its quality of nourishing different species of vegetables, not of the quantity of it. Which quantity may be altered by diminution or superinduction.
So for heat ; our earth when it has in the stove the just degree of heat, that each sort of plant requires, will maintain plants brought from both the Indies.
Plants differ as much from one another in their various degrees of heat and moisture, as a fish differs from a salamander.
Indeed mistletoe will not live upon the earth, until it be first altered by the vessels of a tree, and therein is as nice in food as an animal.
There is no need to have recourse to transmutation ; for whether air or water, or both, are transformed into earth or not, the thing is the same, if it be earth when the roots take it ; and we are convinced that neither air nor water alone, as such, will maintain plants.
I can find no clear proof of the reality of transmutation : the only one that I know is that Sir Isaac offers, for water being transmuted into earth, which he quotes from Mr. Boyle ; but that experiment was made by a friend of Mr. Boyle, and Mr. Boyle himself was so far from believing it a real transmutation that he gave a reason to prove the impossibility of it.
The substance of the experiment here follows : viz., An ounce of
rain-water being distilled near two hundred times, there remained six drachms of white powder, and a considerable quantity of water left behind ; which powder, Mr. Boyle suspects might be partly obtained from the glass vessel wherein it was distilled rather than from the ounce of water, neither the glass nor the remaining water having been weighed ; for if the glass were diminished (which could not be known but by weighing), or if the remaining water were above two drachms, it would have been a demonstration, that all the powder did not proceed from the ounce of water : and I suppose that some part of the water (being volatile, and passing pores that scarce any other fluid does) might get off through the hot glass, or otherwise, in such a number of distillations ; and that then there must be (for supply of that loss) some adventitious matter in the six drachms of powder, though the water that remained should weight but just two drachms.
And this powder must consist of parts of the glass, and of such matter as the distillations had separated from the pores of the water.
Mr. Boyle thinks, that " if water be truly an homogeneal body, it is difficult, if not impossible, to conceive that it can be transmuted : for how (says he) can the bare convention of the parts of a fluid into a concrete, alter the specific gravity ?" Which is as much as to say, that water being specifically lighter, cannot become powder, which is specifically heavier : and water after distillation (being more pure, though never perfectly pure) always becomes specifically lighter than before ; and the matter that is left in the still, heavier ; water changing its specific gravity in proportion to the degree of its purity.
And water considered abstractedly from the charge of other matter (chiefly earth, which it carries in its pores or interstices) is at this time, I think, generally agreed to be homogeneal, consisting of
extremely small, smooth, hard, porous, spherical particles of equal diameters, incompressible, void of taste, and having no quality that renders a body heterogeneous.
But indeed (as far as I am informed), Mr. Boyle and his friend, at the time this experiment was made, did not at all distinguish any difference between the particles (or corpuscles) of water and the other matter contained in its pores (mistaking the vehicle for the thing carried, that which, nothing can be more different) ; and therefore they, as they seem to consider both only confusedly, could have no distinct idea of either ; and thus this experiment proves nothing in favour of transmutation. And yet it has deceived some who, one would think, should have examined more narrowly into the matter than to mistake a separation of earth from water for a change of water into earth.
But this will cease to be a wonder, when we see what that miracle of a man Sir Isaac Newton brings for argument to countenance an hypothesis of his.
" Water (he says) is by heat converted into vapour, which is a kind of air, and by cold into ice, which is a stone ; and this stone is convertible into water again by heat, as vapour is by cold."
But I believe the learned will now subscribe to the opinion, that water, when carried in the air, under the form (or rather name) of vapour, is not air of any kind ; and that when it is under the form of ice it is not rally stone ; it never having all the properties of air, or of stone.
His other instances are of like validity ; for an egg being turned into an animal, is no more a real transmutation, than that the royal oak was transmuted into a prince, when he was taken out of it ; or that a man's house, when he is gone abroad is transmuted into a man.
A maggot is a little fly enveloped in a thin skin, which, as a garment, hides the wings and legs ; and continues to be the same fly when uncovered, as a man is the same man when his garments are off, as when on ; the fly grows bigger, and so does a boy when he becomes a man, but still continues to be the same person, without any real transmutation, unless he should become infallible.
Sir Isaac says, that " all birds, beasts, fishes, insects, trees, and plants, grow and increase out of water, and aqueous and saline tinctures : and on putrefaction all of them revert into water or an aqueous liquor again."
Also in treating of Comets, he says, " They seem necessarily requisite, from whose condensed exhalations and vapours all that moisture, which is consumed in vegetation and putrefaction, and turned into dry earth, may by degrees be continually resupplied and recruited ; for all vegetables do entirely grow and increase from liquors : and then as to their greatest part, do turn, by putrefaction into dry earth, and a slime perpetually is precipitated to the bottom of putrefying liquors."
" From hence the quantity, or bulk of dry earth, must continually increase, and the liquors, or moisture of our globe continually decrease, and, at least, be quite evaporated and lost, if they had not as continual a supply from some part or other of the universe."
Now I must beg leave to confess, that I can see no force in these arguments, either for the transmutation of water, or any such necessity of comets.
And even though transmutation should be supposed (which by no means can be granted), yet no such consequence of the decrease of water on our globe can be drawn from Sir Isaac's argument, but the contrary.
For he says, that birds, beasts, fishes, insects, trees, and plants, on putrefaction, all of them revert into water, or an aqueous liquor again.
How then does it follow, that the water of our globe is ever consumed or diminished, or that it can want any supply of
The water brought to the land in vapour from the sea, we see returns by the rivers to the sea again ; all of it, either before it in parts enters other bodies, or after it return out of them, except such of it that is carried back in vapour.
The smoothness, hardness, and other properties of the corpuscles of water seem to render them incapable of the cohesion which is necessary for incorporating with earth or other bodies, yet where these corpuscles are so very few in number as to lose their fluidity, some of them may rest in other bodies for a time, but afterwards either slide out, or are expelled by heat ; or else more of the same corpuscles come to them, and restore them to fluidity : for it is not likely they should remain always confined by other bodies since their slipperiness, sphericity, and equal smallness of their diameters enables them to pass the pores of gold, and where one corpuscle passes, all may pass ; some sooner, some later, as there are innumerable degrees of dryness and moisture.
A violin is said to require fourscore years after the making ere it obtains that degree of dryness that gives its perfection of sound : and after all, cannot be supposed perfectly dry, whilst it has pores permeable to the aqueous vapour that floats in the ambient air : and some such pores will it have until time (that devourer of things) has destroyed its texture, and reduced it to the very same earth, that water carried in at the vegetable roots ; which earth, will then again become as dry as when water seized it, and took it up for the trees out of which the violin was made. Green wood would grow drier but not lighter, if water were transmuted in it.
I can see no reason to think that any part of the pure element (or corpuscles) of water is consumed upon vegetation ; but rather, that the same water which served for the production, &c. of one plant,
may afterwards as well serve for other plants successively, and for all other its uses as long as the world shall last : nor do I think there is any diminution of that element on our globe since it was first created ; for as much water going out of some bodies as goes into other, keeps the quantity the same, and the balance even betwixt it and earth, without a necessity of any supply from comets.
From Sir Isaac's transmutation-arguments we may learn, that a man never ought to depend entirely upon his own for support of his own hypothesis.
Sir Isaac's death seems scarce a stronger proof of his being human, than the whole contexure of these arguments is. To favour transmutation, he says, the bodies of animals and plants, on putrefaction, revert into water or an aqueous liquor again ; but in favour of the necessity of comets, on account of the consumption of water, he says, that those bodies turn by putrefaction into dry
It is difficult for the ignorant to understand the terms of the learned, but, by this aqueous liquor, I understand a mixture of earth and water, and suppose a saline tincture is only a term of the learned of the same signification ; but that a liquor and dry earth should be the same thing, is what, I own, I can be no means comprehend.
It is certain that by the consumption of water, Sir Isaac does not mean the annihilation of it, but that is was transmuted into dry earth.
If this were so, an animal or vegetable would weigh as much when putrefaction had reduced it to dry earth as it would when living.
Yet, we find, that this remaining dry earth is only a very small part of the weight of the living animal or plant.
What then becomes of the remainder of the whole weight, whereof the living bodies consisted ?
Why, I suppose it goes the same way that the aqueous part of the nourishment of a living body goes, after a short stay therein, viz., it either perspires into the atmosphere, or sinks into the ground, all except what remains for increase of the bodies, which is but a very inconsiderable part of the water, and none at all when the bodies are at their full growth, or declining.
I cannot conceive how the liquors or moisture of our globe, should ever be all or in any part lost by being evaporated, unless it should fly off to some other part of the universe, instead of being continually supplied from thence.
Were it not for evaporation, the watery element would be useless to vegetables and animals, except to such as live with salt-water in the sea ; for neither springs, nor rivers, nor other fresh water would be found on our globe : or, if so great a quantity of liquor or moisture should be transmuted into dry earth, and resupplied from any other part of the universe, the bulk and diameter of the earth must continually increase ; and what consequences such an increase might have is above my inquiry ; but I suppose the attraction to the sun would continually increase in proportion to the access of matter continually coming to our globe.
But what alterations such increased bulk and weight might cause in the motion or orbit of this our planet astronomers can only
judge ; and I am not informed that any of them have ever observed any increase of the earth's diameter, &c.
As far as this hypothesis of Sir Isaac's relates to agriculture I think we need not fear it, so as to abstain from raising as many vegetables as we can ; there being no danger of their consuming the water they imbibe, for in general we have rather too much water than too little ; and it is observed, that three or four wet summers make a scarcity, and many dry ones make a plenty in our islands : and if it were not the same in other countries, wet summers would not cause the price of corn here to be treble what it is reduced to by dry summers.
We have therefore more to fear than hope from the tails of comets, because the matter of them mixing with our atmosphere would be likely to bring both famine and pestilence amongst the inhabitants of our earth ; the former by the aqueous part, and the latter by the noxious terrene exhalations of which, as well as of watery vapours, the tails of Comets are supposed to consist.
It is allowed that the fine particles of earth, &c. brought to the ground by water, enrich the soil ; but yet much water in the growing season is very pernicious to corn, though not to weeds, they being naturally adapted to the soil, some of them aquatics, some amphibious, and others that cannot bear so much water, grow on such lands whereon the water did not long remain, but sinks down or runs off very soon.
I may add, that if the intense heat of actual fire, in almost 200 distillations be not able to break the corpuscles of water, or destroy their texture, so as to change that element into earth, or any other matter, there can be no possibility of such a transmutation from that very small degree of heat which water suffers by the weak ferment it encounters in the vessels of plants and animals.
These kind of metamorphoses may properly enough be considered in dissertations purely concerning matter, and to discover what the component-particles of earth are ; but not at all necessary to be known, in relation to the maintaining of vegetables.