it will produce sterility, disease, and death; and if it be too open and dry, it will, by permitting the water to drain off too rapidly, and by its incapacity to return it, rob the soil of its carbonaceous principle, and render it sterile.

No doubt, with vegetables as with animals, the quantity and quality of the food, and the protection and support afforded, determine their capacity and produce; therefore, in the course of cultivation, all arrangements must be made to accord with the object in view; and in this, our desires must conform to our means: it will be wasteful folly to provide a bed or couch, and food sufficient for a large tree, when we have space or room only for the trunk, branches, &c. of a small one, and the

reverse.

53

ON THE

SAP OF TREES,

ITS RISE AND CIRCULATION.

UPON what principles, and by what application of power, the rise of the Sap from the Roots, and its distribution and transformation into the different parts and produce of the Tree, is conducted, is a question that has long been in agitation, and which has given rise to much speculation, argument, and difference of opinion, among the learned.

Many describe the Sap in vegetables as circulating, like the blood of animals, through an appropriate system of vessels, whilst others deny the possibility of such circulation, or even the existence of such vessels.

Bradley says, "The many curious observations which have been made concerning the structure of animal bodies, and what Dr. Grew, Malpigius, and myself have remarked, in the structure of vege tables, may ascertain to us that life, whether it be animal or vegetable, must be maintained by a due circulation and distribution of juices in the bodies they are to support. And proceeds to explain his opinion, "That the Sap circulates in

the vessels of Plants, much after the same manner, as the blood doth in the bodies of animals." And after a variety of abstruse argument, he says, "In fine, a Plant is like an Alembic which distils the juices of the earth; as for example, the Roots having sucked in the salts of the earth, and thereby filled itself with proper juices for the nourishment of the Tree, these juices then are set in motion by the heat, that is, they are made to evaporate into steam, as the matter in a still will do when it begins to warm. Now as soon as this steam or vapour rises from the root, its own natural quality carries it upwards to meet the air; it enters then the mouths of the several arterial vessels of the Tree, and passeth up them to the top, with a force answerable to the heat that put it in motion: by this means it opens little by little, as it can force its way, the minute vessels, which are rolled up in the bud, and explain them by degrees into leaves; thus when we give a forcing heat to the root of a Plant, it grows quicker than when it has only a moderate heat; but as every vapour of this kind, when it feels the cold, will condense and thicken into water, so when the vapour which I mention to rise through the arterial vessels, arrive at the extreme parts of them, i. e. the buds of a Tree, it there meets with cold enough to condense it into a liquor, as the vapour in a still is known to do; in this form it returns to the root down the vessels which do the office of veins, lying between the wood and the inner bark, leaving, as it passeth by,

such parts of the juices as the texture of the bark will receive and require for its support.'

Miller says, "The notion of the circulation was entertained by several authors much about the same time, without any communication one to another, particularly M. Major, a physician at Hamburgh, M. Peracelt, Mariotte, and Malpighi: it has met however with some considerable opposers, particu. larly the excellent M. Doddart, who could never be reconciled to it.

"M. Doddart, instead of the same juices going and returning, contends for two several juices, the one imbibed from the soil, digested in the root, and from thence transmitted to the extremes of the branches, for the nourishment of the Plant; the other received from the moisture of the air, entering in at the extremes of the branches, so that the ascending and descending juices are not the same." And he further says, "In opposition to the notion of circulation of Sap in Trees like to that in animal bodies, the Reverend Mr. Hales, in his Vegetable Statics, presents us with various experiments."

Forsyth is evidently an advocate for the circulation of Sap: he says, "The Sap will always find its way first to the extremity of the shoots, and the spurs will only receive it in small proportion, as it returns from the end of the branches."

Mr. Knight is also an advocate for the doctrine of circulation, and has published a variety of papers, reciting a number of experiments that he has

made, and which he considers to confirm the fact; and Sir H. Davy conforms to his opinions. He says, "In all plants there exists a system of tubes or vessels, which in one extremity terminate in the roots, and at the other in leaves. It is by the capillary action of the roots, that fluid matter is taken up from the soil. The Sap, in passing upwards, becomes denser, and more fitted to deposit solid matter; it is modified by exposure to heat, light, and air, in the leaves; descends through the bark; in its progress produces new organized matter, and is thus, in its vernal and autumnal flow, the cause of the formation of new parts, and of the more perfect evolution of parts already formed."

But Mrs. Ibbotson, who appears to possess ample means, and sufficiently extensive powers, for ascertaining the fact, by dissection and examination with a very powerful solar microscope, after explaining a variety of observations which induce her to conclude that the Sap does not circulate, says, "How strange, then, to alter all this beautiful arrangement, justified, indeed taught, by dissection, in order to find a place for Sap vessels, that cannot possibly require any; for why must they have returning vessels? Is there not a great difference between an animal, which after the first few years has no increase, and a being that increases from every joint, and is supposed, therefore, to draw up only those juices necessary for that increase; espe

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