the Rain Water mixed with the other Principles which compofe Plants, being joined and contiguous to their Roots, finds there imperceptible Pores through which it infinuates it felf, and its return is obftructed, which is the cause that this firft Sap is preffed always on in Plants.

It has fome refemblance with the Chyle, and becomes analogous with the Blood of the Veins, in proportion as it mingles with the best prepared Juice that is already there, and which is almoft like that which the Body of the Seed gives in the beginning.

This firft entrance of the Water into the Roots is caufed by a Law of like nature with the motion of union, of which I have spoken elfewhere; for where-ever there are very ftrait and narrow Tubes which touch the Water, it enters therein and rifes alfo against its natural inclination to defcend.

For an Example of this, take a very narrow Tube of Glafs, and very clean, put one of the ends of it into Water, it will rife to a confiderable height above its level; put one end of a Sugar Loaf into a little Water, it will rife up to the top in a little time; but it will not rife in Glafs Tubes rubbed with Tallow, or if through time they have acquired a certain foulnefs, as is that of Varnish to which Water will not stick, for it is not enough that the Pores are difpofed to let the fubtile Parts of other Bodies enter, they must also be pushed thither by fome Principle of Motion: But whatever be the Cause of the Effect, vulgarly called Attraction, it is enough that it is very common, and that Chymistry furnishes us with a great many Examples

of it.

MARCH 1731.

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The firft Juice ill-digefted is not proper to nourish the principal parts of Plants; but according to the analogy of the Vegetation of Animals, it ought to perfect it felf in paffing through Tubes of different ftructures, as the Blood perfects it felf in paffing through the little Veffels of the Lungs, the Liver, feveral Glands, &c.

The better to judge of the Truth of this fimilitude, I cut long-ways and across feveral Stalks of Milky Plants, and of fuch as have a yellow Juice, and I obferved that all the Humour contained in these Plants was not coloured, but only that which was contained in certain Canals which I compare to Arteries; I confidered feveral times the Structure of thofe little Canals, and found that each of them have in the middle a fmall white ligneous loofe Fibre, and which may be feparated into feveral Filaments; that there is a fmall Membrane round about these little Canals, which separate them from the rest of the Stalk, and makes of it as it were a little Tube, and that between each of the Fibres, and the Membrane which furrounds them, there is a fpungeous Matter adhering to the Membrane, and full of coloured Juice, which we may easily discover by means of a Convex Glafs, which is made ufe of to magnify Objects; for the extremities of thefe Fibres being cut they appear white, and divided into little Filaments, and then we fee the coloured Juice iffue out from feveral places of this fpongeous Matter when it is cut off and broken.

The reft of the Stalk is full of another spongeous Matter, full of a watery infipid Humour without colour, and of a very fluid confiftence, whereas the coloured is fomewhat thick and ve

ry

ry picquante in feveral Plants. We fee the like ftructure in the Leaves of Aloes when we cut a Leaf of it acrofs; for we find the middle, which is about an inch thick, is of a fpongeous fubftance, compofed of a great number of Membranes confounded together, of a clear watery Humour which has very little bitterness; we obferve also that the fpongeous fubftance is covered with a green Skin, in the thickness of which there are a great many blackish Canals difpofed long-ways upon the Leaf, like thofe of milky Plants. Thefe Canals contain a viscous, yellowish, and very bitter Juice, which iffues abundantly therefrom in the Month of May; but in the Pulp, or spongeous fubftance, there are a great many whitish Canals which apparently contain another Juice, and which caft out here and there little Boughs, fome of which go and join themfelves to the Tubes which carry the yellow and bitter Juice.

I have moreover obferved, that a great many grofs milky Plants, as Ferula or Fennel Giant, have thefe little Canals difpofed by equal intervals from the Centre of the Stalk to the Circumference; and the greatest part of other Plants, as the Salfifix, Tithymalle, Celandine, &c. have only two or three Rows of them near the Circumference of the Stalk. Thefe Canals, with their white Fibres, and their spungeous Matter full of coloured Juice, continue themselves from the Stalk to the Branches, and the extremities of the Leaves, where they make of them a Tiffue in the Figure of Nets, which forms that nervure or boffing we fee in dryed Leaves, and even too in thofe that are green. They extend themfelves likewife to the Roots. The fhining Angelica of Canada fhews them veM 2

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ry diftinctly; for in the middle of fome of its Branches, which are generally channelled, we fee one or two of them which are disjoined from the reft, and are contiguous only at the Knots and Angles of Ramification.

It is eafy to judge that the Liquor contained in thefe little Canals, is that which nourishes the principal Parts of the Plant, as the Bloffoms, Flowers, Fruits, Seeds, &c. and that it has a fimilitude with the arterial Blood; that what is in the rest of the Stalk is analogous to the Blood contained in the Veins, and that the Fibres which are in the middle of the little Canals, ferve to keep them firm, and hinder them from plying or breaking, for if they were plyed down, the course of the Sap would be interrupted; and we ought to hold it for certain, that thofe Plants which have no coloured Juice, are not without fome Canals, with a Sap different from that which is in the rest of the Plant.

Now as in the external part of the Roots. there are imperceptible Pores through which the Sap paffes, which I have compared to the Blood of the Veins after it has been prepared by the heat of the Sun, and by the filtration there made of it through the spongeous Matter which is in the rest of the Plant: The return of this Sap is hinder'd as well as that which enters into the Roots; whence it happens that the Liquor intermixed in thefe little Canals is ever extremely preffed, which ferves to make the Branches, Leaves, and Roots extend themselves. This is proved by feveral Experiments.

If we cut tranfversely a milky Plant, or one of the Cells which contain the yellow Juice, we always fee as much or more of the coloured Juice come from the Part where the Leaves are, than

from

from that where the Root is, even though we hold the pluck'd-up Plant the Root upwards before we cut it; and if we cut the extremity of the Root, there alfo iffues out of it a good deal of coloured Juice, as well as from the extremities of the Leaves, or the little Branches when they are alfo cut; which evidently fhews that this Juice is very much preffed in these Canals, as the Blood is preffed in the Veins and Arteries; and that this compreffion makes the Roots extend as well as Branches and Leaves; and in fhort, that it would not be fo much preffed, if the Juice did not enter through Pores fo difpofed as to hinder its return.

If we afterwards cut the reft of the Stalk about an Inch below the first incifion, we fhall alfo fee the coloured Juice which comes from the Roots rife up; but we fee nothing, or very little of it in the upper part of it, which muft neceffarily happen if there were fmall Pores in the Canals through which the Juice extends it felf towards the Roots, fince they no longer receive any of it from the Leaves and Branches: And for the fame Reafon if we cut a little of the part where the Leaves are, higher than the firft incifion, we must not expect to fee any Juice, or very little, rife up from the little feparated part, but it must always neceffarily defcend from thofe where the Leaves are; which I found agreeable to experience, particularly in the Herb called Dentdelion, Celandine, and in the Stalks of Tithymalles or Milk-thiftles. I remember I have often obferved to you the fame things in fome of thefe Plants.

We might conjecture that after the first Juice contained in the little fibrous Canals has fufficiently nourished the parts of the Plant, the over

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