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[4]. 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.
[4]’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.