« AnteriorContinuar »
The first Juice ill-digested 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 self in passing through Tubes of different structures, as the Blood perfects it felf in passing through the little Vessels of the Lungs, the Liver, several Glands, &c.
The better to judge of the Truth of this fimilitude, I cut long-ways and across several Stalks of Milky Plants, and of such as have a yellow Juice, and I observed 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 considered several times the Structure of those little Canals, and found that each of them have in the middle a small white ligneous loose Fibre, and which may be separated into several Filaments; that there is a small 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 surrounds them, there is a spungeous Matter adhering to the Membrane, and full of coloured Juice, which we may easily discover by means of a Convex Glafs, which is made use of to magnify Objects; for the extremities of these Fibres being cuc they appear white, and divided into little Filaments, and then we see the coloured Juice iffue out from several places of this spongeous Matter when it is cut off and broken.
The rest of the Stalk is full of another spongeous Matter, full of a watery infipid Humour without colour, and of a very fuid consistence, whereas the coloured is somewhat thick and ye
ry picquante in several Plants. We see the like structure in the Leaves of Aloes when we cut a Leaf of it across ; for we find the middle, which is about an inch thick, is of a fpongeous substance, composed of a great number of Membranes confounded together, of a clear watery Humour which has very little bitterness; we observe also that the spongeous substance is covered with a green Skin, in the thickness of which there are a great many blackish Canals disposed long-ways upon the Leaf, like those of milky Plants. These Canals contain a viscous, yellowish, and very bitter Juice, which issues abundantly therefrom in the Month of May; but in the Pulp, or spongeous substance, there are a great many whitish Canals which apparently contain another Juice, and which cast out here and there little Boughs, some of which go and join themselves to the Tubes which carry the yellow and bitter Juice.
I have moreover observed, that a great many gross milky Plants, as Ferula or Fennel Giant, have these little Canals disposed by equal intervals from the Centre of the Stalk to the Circumference; and the greatest part of other Plants, as the Salsifix, Tithymalle, Celandine, &c. have only two or three Rows of them near the circumference of the Stalk. These 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 bossing we fee in dryed Leaves, and even tog in thote that are green. They extend themselves likewise to the Roots. The Shining Angelica of Canada shews them ve
ry distinctly; for in the middle of some of its Branches, which are generally channelled, we see one or two of them which are disjoined from the rest, and are contiguous only at the Knots and Angles of Ramification.
It is easy to judge that the Liquor contained in these little Canals, is that which nourishes the principal Parts of the Plant, as the Blossoms, Flowers, Fruits, Seeds, &c. and that it has a similitude 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, serve 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 those 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 passes, 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 fpongeous 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 these little Canals is ever extremely pressed, which serves to make the Branches, Leaves, and Roots extend themselves. This is proved by several Experiments.
If we cut transversely a milky Plant, or one of the Cells which contain the yellow Juice, we always see as much or more of the coloured Juice come from the Part where the Leaves are, than
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 also issues 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 also cut; which evidently shews that this Juice is very much pressed in these Canals, as the Blood is pressed in the Veins and Arteries ; and that this compression makes the Roots extend as well as Branches and Leaves; and in fhort, that it would not be so much pressed, it the Juice did not enter through Pores so disposed as to hinder its return.
If we afterwards cut the rest of the Stalk about an Inch below the first incision, we shall also see the coloured Juice which comes from the Roots rise up; but we see nothing, or very little of it in the upper part of it, which must necessarily happen if there were small Pores in the Canals through which the Juice extends it self towards the Roots, since they no longer receive any of it from the Leaves and Branches : And for the same Reason if we cut a little of the part where the Leaves are, higher than the first incision, we must not expect to see any Juice, or very little, rise up from the little féparated part, but it must always necessarily descend from those 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-thistles. I remember I have often observed to you the same things in some of these Plants.
We might conjecture that after the first Juice contained in the little fibrous Canals has sufficiently nourished the parts of the Plant, the over
plus, is resumed by the spungeous Matter of the Plant, to be reunited with the other Juice, and re-enter afterwards several times into the little Canals by a continual circulation, but I dare not affirm it for a certainty; and much less that there are different Pores, some of which carry the Juice to the Root, and others to the Branches ; but I hold it for an undoubted truth that the watery Juice passes into the little Canals, whence it is pushed towards the Root and Leaves, after having been mingled with the other, and taken the same Dispositions as the Chyle, which is white, by entering into the axillary Vein, becomes by little and little like Blood, and repairs it. I believe also that the same thing happens to Trees, that is to say, that they have different Canals between the Bark and the Wood, &c. and that they are nourished after the same manner.
The first Juice which comes from without, does not enter only through the Root into Plants, but also through the Leaves and Branches, and they receive it from the Dew or Rain, or Vapours which the air is always full of; which I have found to be so by the following Experiments.
If we cut a small Branch of a Tree, or some Herb, as Parsley, Cerfeüil, (called otherwise Chervil) &c. where there is some ininute Branch growing at the side, and soak the extremities of the Leaves in Water, letting the Stalk with such little Branch lie upon the brim of the Veffel where the Water is, this little Branch will continue green three or four Days, even in Summer; and if it be of Baume, which is an odoriferous Herb, it will continue above fifteen Days as green as in the Garden, and grow a