CHAP. XVIII.

AS I am of Opinion, First, That there is in the Spring, a certain Rarefaction in all Vegetables, which is the first Mover in Vegetation. And Secondly, That there is in every Plant a Vital Principle, which being a necessary Agent, re∣ceives the first Effects of that Rarefaction, as I have already discoursed elsewhere. So I cannot think of any Comparison fitter, to make my Notion intelligible, than that of a Clock, which needs no more to set it going, than only to pull up the Weight, and give a little Jog to the Pendulum—The Truth is, I always thought it absolutely impossible to make this pretended Circulation consistent with the Action of the Roots, which we daily see to extend themselves both in Length and Thickness at the very same Instant that they receive their Nourishment. And the Objections that prevail'd with me, were these.

First, I cannot apprehend either at what time, or in what Place this Circula∣tion should begin. Secondly, I cannot see either any Necessity, or Advantage of it. Thirdly, Supposing we should admit it, I am in the dark, whether we must assert one general Circulation only in every Tree, or whether there must be as many Circulations, as there are particular Branches, &c.

As for the Time when it begins, if there be such a Circulation, it must certainly have its Beginning the very same Instant that the Roots begin their Action, and al∣so must owe that very Beginning to the Influence and Virtue of the Roots; so that consequently there may be a Time when there will be no Circulation, for as much as the Roots are not continually in Action. Now, as the principal Reason of ad∣mitting this Hypothesis of Circulation in Animals is drawn from the Necessity of it, viz. for the Purifying the Blood, which, we are told, would be in great Danger of being corrupted, if not kept in continual Motion: So if that Instance hold in Plants, it must then also follow, that the Sap would be in the like Danger of Cor∣ruption, that very first Moment of its Circulations being intermitted; and conse∣quently we should see a general Mortality of all those Trees that should happen not to be in Action; whatever the Cause of it might be, whether their being hindred by the Frost, or their lying out of the Ground; and much more, that all Branches, when once separated from the Tree that bare them, must immediately perish; just as the Members, as soon as they are cut off from the Body. But now there is no∣thing more contrary to the Experience of every one, than this will, as appears evidently by that infinite Number of Plants, and Grafts, which are so frequently, and with such good Success, sent into foreign Countries, without the least ill Accident, provided they be not overmuch dry'd by excess of Heat.

But supposing there be really such a Circulation, and that it commences at the same time with the Action of the Roots: Yet how will they be able to solve the Production of those Branches which shoot forth in the Spring, without any Depen∣dance upon the Roots. That it is so, there can be no doubt, since we have Instan∣ces of it every Spring in Trees newly planted, and which have not yet put forth any new Roots. As also in Trees digg'd up in the Winter, and left lying on the Ground: and even Branches lopp'd off in that Season, and set up an end in the Ground, will put out little Shoots in the Spring.

In fine, How is it possible to give a clear Account of this Circulation, when we find that Almonds, Nuts, and even common Seeds, shoot out within the Earth, and in a few days put forth a Root, growing in length downward, but do not cause a∣ny Production to rise up out of the Ground? When we see that, the Bulb of the Imperial will send out Roots in August, but no Stalk; and on the contrary, other Bulbs put out Stalks in the Autumn and Spring, but no Roots; when Tulips, Tube∣rose's, and especially the Asparagus, grow upright in such a manner, as that which was the extream Part at its first Appearance, still continues so, and that all of it rises entirely and at once from the Bottom to the Top; when the Sprouts shooting out from the Extremity of a Branch, which has been cut or cropt, have such an ex∣tream difference in Length and Thickness, as I have formerly described. It is, I think, sufficiently clear from hence, that there is a very unequal Distribution made of the Sap; seeing that the Fruit-buds are form'd only upon the Top of the weak Branches, and grow only at the Bottom of the Strong. I must confess, it seems a Page  70 very difficult Task to me, to prove a Circulation in all these, and an infinite Num∣ber of other Examples, that I could produce upon this Occasion.

If we can prove therefore that there is no Circulation in some Plants, I see no reason why we may not positively conclude against the Admission of it in others.

But to give a further Demonstration of the Impossibility of this Circulation, let us but consider, that upon the Admission of it, we must suppose in every Branch, three distinct, and separate Passages, viz. two for the going, and returning of the imperfect Sap, and a third for the return of it when it is arriv'd at its Perfection, namely, to convey it to that Place where it is to make its Residence. I do not say there must be Passages for its Rising and Descending, because it happens very fre∣quently, that the Branches hang downward, and Fruit-Branches generally grow in that Posture; so that to speak properly, we cannot say that the Sap Ascends, when really it Descends; and for this Reason I chose rather to say barely, that the Sap will need several Ways or Passages for the Conveyance of it in its going and return.

For Instance, I desire to know where they will find these three distinct Passages in a Cherry-Stalk, or how the Sap, which in its first Motion, should have risen to the Extremity, or Top, and then return'd back immediately down to the Roots: how I say it should be determin'd by Nature, to descend to the Cherry, which hangs down, and afterwards re-ascend to that Place, where it turn'd out of the way that lead it upward, and from thence fall into that Path which was to convey it to the Root, and at last re-conduct it to the Place where it is finally lodg'd, to supply the Exigencies of the Fruit and Leaves.

I would ask further, Whether or no there be not a Circulation of Sap in the Fruit, as well as in the Tree; if so, then these two Saps, must, in their Return, have each of them their particular Way (which will cause a great Multiplication of Ways) or else they must necessarily mix together, and then would ensue an un∣lucky Confusion of the two Saps, one of which is affirm'd, by them, to be much Purer and Nobler than the other.

According to this Hypothesis, the Sap must make a great many Journeys backward and forward, which is a thing very disagreeable to Nature, who affects to be plain and simple in all her Operations. Why therefore may we not rather say, that the Sap acquires its Perfection that very Moment in which it arrives at the Roots; just as the Air is illuminated in every part, immediately upon the Sun's beginning to ap∣pear above the Horizon? But further, admitting that this Circulation were necessary for perfecting the Sap, I would fain be satisfy'd where it is that the Sap receives this Perfection. It cannot be at its first entrance into the Roots, because, according to the Principles of our Antagonists, it is there but in an imperfect and indigested State; neither can it be when it is arrived at the Extremities of the Boughs, or Fruit, seeing it doth not continue there, but has yet two Stages to travel further; for if it take up its Rest in those Extremities, it must then follow, that it was come to its compleat Perfection, and consequently would have no need of returning to its first Sourse. Neither can it be said to be thus perfect at its second coming into the Roots, because then certainly it would take up its final Residence with them; for since it is indifferent to the Sap, when it is once perfectly digested, whether it be employed in the Formation of the Roots, Trunk, or Branches, Leaves or Fruits; it would undoubtedly fix it self in the very first Place, where it should find it self qualified with all the Degrees of Perfection requisite to its Nature.

Again, Supposing that the Extremity, or Top of the Branch, to which the Sap was to have risen, were cut off, I desire to know in what manner this Communi∣cation of Ways, and turning out of the one into the other, could be solved, and what would become of the Sap design'd to have been made into Fruit, if it should be stopp'd in the midst of the Way, before it could arrive at its Journey's End.

It cannot be deny'd that this Doctrine of Circulation, draws an infinite Number of Inconveniencies along with it, which, in my Judgment, can be prevented no other way, but by the following Account of the Process of the Sap in Vegetation, viz. That the Vital Principle, which is the First Mover in the Action of the Plant, being Invigorated by the Warmth of the Sun, immediately communicates to that Moisture, which was attracted by the Roots, such a Quality as is necessary to the making of it perfect Sap, which nevertheless is not determined in its own Nature, to any particular. Production, but may indifferently become either Fruit, Leaves, or Trunk; and as that Sap has all the Degrees of Rarefaction that are requisite for Page  71 it, it must necessarily be a light and subtil Body, and consequently extreamly a∣dapted to rise up to all the Extremities of the Branches. Where it is very plenti∣ful, it exerts it self, in producing a great Number of Boughs, and Leaves, all of them bearing a Size proportionable to the abundance of the ascending Sap: If it ascend but in a very small Quantity, it is employ'd in bearing an infinite Number of Blossoms, and good store of Fruit, though it will be but small in its Dimensions. And lastly, where the Sap rises in a moderate Proportion in some certain Places, as either upon the Top of the weak Branches, or the lower part of the Strong, it there signalizes it self in the Productions of Buds, and of large and beautiful Fruit.

But now to give a clear and rational Account of this admirable Distribution of the Sap unto every part of the Tree, either for the Beginning, Continuing, or Com∣pleating, and Determining it in its just Bigness and Proportion, is a Work above Humane Performance. Nature seems expresly to have deny'd us that Priviledge, as if she had seem'd industriously to hide from us, under a thick Veil, the Manner, both of her Conception and Production; so that hitherto, our ordinary Faculties have not been able to fathom this mysterious Subject of Vegetation.

I will not deny but that there is a Circulation of the Blood in all Animals; for∣asmuch as the Vessels with their Extremities and Insertions, and indeed the whole Structure of their Body is so exactly entire, and perfect in all its Extent, as that we cannot conceive an abrupt Beginning or End of them. Hence it is that they are so excellently fitted for the Reception of the Blood and Spirits, and restraining them from issuing out at any Extremity. But in Trees, whose encreas∣ing in length is continually form'd outwardly, we must suppose the Vessels to be o∣pen at their Extremities, and that they receive their Augmentation in length, on their Outside, as the whole Mass of the Tree doth; so that there is no Analogy between the Vessels in the Body of an Animal, and those in a Tree, and conse∣quently the Inference deduced from that Comparison, must needs be erroneous.

The third Question, wherein I desire to be satisfy'd, viz. Whether, upon sup∣position that there be such a Circulation, we must say that there is but one general Circulation in each respective Tree, or else that there are as many particular Cir∣culations as there are Branches, is perhaps as difficult to resolve as any. For if we admit but one in general, we shall be hard put to it to give an Account how a Slip set in the Ground, comes to take, so as in a short time to become a perfect Tree. We must be forc'd to say, that in every one of these Branches there was a true Cir∣culation, which ceas'd from Action as soon as they were cut off from the Tree up∣on which they grew; but that as soon as by their Re-plantation they were restor'd to a Condition of Acting of themselves, their Circulation also began to resume its Action; and by these Steps they came to be perfect Trees.

If therefore, to give a Reason for this Growth of Slips, we must admit of a particular Circulation in every Branch, we must likewise be forc'd to admit of ma∣ny Circulations in every Branch. For since any Branch may be divided into seve∣ral Parts, if every one of these Parts be set in the Ground, with all the due Circum∣stances belonging to them, they will as easily take to grow, as if they had been entire Branches. But this Solution will draw us into a Progressus in infinitum, than which, in Ratiocination, nothing can be more absurd.

Thus, when a Layer of a Vine being put into the Ground, takes a new Root, and thereupon that Part of the Layer next to the Earth, which before was the smallest, becomes in a little time thicker than the Part next adjoyning to the Tree: Must we not of necessity have recourse to a new Circulation, since the former seems plainly to be at an end, or at least to have become altogether useless I must confess, I cannot find any Expedient of adjusting all these particular Circulations, with the general one, to make them act in Conformity with, and Subordination to it, when they are all together in the same Tree at the same time.

Such a Cloud of Difficulties and Inconveniencies have prevail'd with me not to give any Credit to this new Opinion of the Circulation of the Sap, though I have at the same time an extreme Veneration for those Worthy and Learned Persons, who are the Authors of it.