HE Motions also of Trunks are various. Principally Four; sc. Ascending, Descending, Horizontal, and Spiral. The cause of the Ascent of a Plant, is a certain Magnetick Correspendence betwixt the Aer and the Aer-Vessels of a Plant; the Motion and Tendency whereof, the whole Plant follows. This I have asserted, and I think, clearly demonstrated in my First and Second Books of the Anatomy of Plants. I will here add this plain Experiment.
2. §. Take a Box of Moulds, with a hole bored in the bottom, wide enough to admit the Stalk of a Plant, and set it upon stilts half a yard or more above ground. Then lodg in the Mould some Plant, for Example a Bean, in such sort, that the Root of the Bean standing in the Moulds may poynt upwards, the Stalk towards the ground. As the Plant grows, it will follow, that at length the Stalk will rise upward, and the Root, on the contrary, arch it self downward. Which evidently shews, That it is not sufficient, that the Root hath Earth to shoot into, or that its Motion is only an Appetite of being therein lodged, which way soever that be: but that its nature is, though within the Earth already, yet to change its Position, and to move Downwards. And so likewise of the Trunk, that it rises, when a Seed sprouts, out of the Ground, not meerly because it hath an Appetite of being in the open Aer; for in this Experiment it is so already; yet now makes a new Motion upwards.
3. §. BUT although the Natural Motion of the Trunk be to Ascend; yet is it forced oftentimes to Descend. For the Trunk-Roots growing out of some Plants near the ground, and shrinking thereinto, like so many Ropes, do pluck the Trunk annually lower and lower into the ground together with them; as may be seen in Scrophularia, Jacobæa, and many other Plants.
4. §. IF these Trunk-Roots break out only about the bottom of the Trunk, as in the aforesaid Plants, then the Trunk gradually Descends into the Earth, and is turned into a Root. But if it be very slender, and the Trunk-Roots break forth all along it, then it Creeps horizontally; the said Roots tethering it, as it trails along, to the ground; as Strawberry, Cinquefoyl, Mint, Scordium, &c.
5. §. AS to their Spiral Motion, it is to be noted; That the Wood of all Convolvulus or Winders, stands more close and round together in or near the Center, thereby making a round, and slender Trunk. To the end, it may be more tractable, to the power of the external Motor, what ever that be: and also more secure from breaking by its winding Motion.
6. §. Wherefore, Convolvulus do not wind by any peculiar Nature or Genius, which other Trunks have not; but because their Parts are disposed so, as to render them more sequaceous to the external Motor. Even as the Claspers of a Vine, having the like Structure, have also a Motion of Convolution: whereas the Branches themselves upon a contrary account, move in a straight Line.
7. §. The Convolution of Plants, hath been observed only in those that Climb. But it seems probable, that many others do also wind; in which, the main Stalk, is as the Axis to the Branches round about. B. 2. P. 1. Ch. 1. Of which number, I conceive, are all those whose Roots are twisted; a Motion we observed in speaking of the Root. Whether it be so, or not the Experiment may easily be made by tying a Thred upon any of the Branches; setting down the respect it then hath to any Quarter in the Heavens: for, if it shall appear in two or three Months, to have changed its Situation towards some other Quarter; it is a certain proof hereof. And that hereby the Roots of many Plants become twisted; the Motion beginning in the Stalk, and ending at the bottom of the Root, which stands always fixed in the same place.
8. §. The Convolution of Trunks, is made not one, but divers ways; some moving by South from East to West; and others from West to East. Wherefore it seemeth, that as the Efficient Cause of Convolution, is not within the Plant, but external: so also, that it is not One, but that there are Two Great Efficients of this Motion; sc. the Sun and the Moon. Some winding together with the Sun, in its Diurnal Motion, (or, if the Earth moves, then, Inclining to the Sun) by South from East to West. And others winding with the Moon, in its Monthly Motion, from West to East.
9. §. This possibly, may also be one sensible way of distinguishing betwixt Solar, and Lunar Plants. Thus far, in general, of the Motions of Trunks.