Part 5

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. 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.

’Tis certain, that Roots and other Chyle Vessels of a Plant have a free Communication throughout 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 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.

CHAP. II.

Of FOOD of PLANTS.

The chief Art of an Husbandman is to feed Plants to the best Advantage; but how shall he do that, unless he knows what is their Food? By Food is meant that Matter, which, being added and united to the first Stamina of Plants, or Plantulæ, which were made in little at the Creation, gives them, or rather is their Increase.

’Tis agreed, that all the following Materials contribute, in some manner, to the Increase of Plants; but ’tis 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 talk’d 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 apply’d to the Root of a Plant, it will kill it as certainly as a Knife misapply’d will kill a Man: Which proves, that Nitre is, in respect of Nourishment, just as much the Food of Plants, as White Arsenick 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, no body has, that I know of, maintain’d 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 affirm’d, 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 publish’d this Phantasy, which at present seems to get Ground, ’tis fit he should be answer’d: And this will be easily done, if I can shew, that he has answer’d 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 dry’d Two hundred Pounds of Earth, and planted a Willow of Five Pounds Weight in it, which he water’d with Rain, or distill’d 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 diminish’d about two Ounces in its Weight.’

On this Experiment Mr. Bradley grounds his Airy Hypothesis. But let it be but examined fairly, and see what may be thence inferr’d.