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.