“I told you,” said James, “I had the true temperance cordial at home—do you not see it in the simple prosperity by which, owing to the blessings of temperance, I am surrounded?—do you not see it in the rosy cheeks of my children, in the smiling eyes of my wife—did I not tell truly that she helped to make it? Is not this a true cordial,” he continued, while his own eyes glistened with manly tears, “is not the prosperity of this cottage a true temperance cordial?—and is it not always on draught, flowing from an ever-filling fountain? Am I not right, Andrew; and will you not forthwith take my receipt, and make it for yourself? You will never wish for any other: it is warmer than ginger, and sweeter than anniseed. I am sure you will agree with me that a loving wife, in the enjoyment of the humble comforts which an industrious sober husband can bestow, smiling, healthy, well-clad children, and a clean cabin, where the fear of God banishes all other fears, make
THE TRUE TEMPERANCE CORDIAL!”
THE SAP IN VEGETABLES.
FIRST ARTICLE.
Botanists describe two kinds of vegetable sap; the one is called the ascending or unelaborated sap, the other the descending or elaborated sap. If a young branch be cut across in the spring season, the newly exposed surfaces will be found rapidly to cover themselves with a dew, especially that portion which is continuous with the trunk—this moisture is the ascending sap: while if during the summer or autumn a piece of twine be tightly drawn and knotted round a young branch of lilac, the part above this ligature will shortly become swollen, and will bulge out on every side, in consequence of an impediment having been thus presented to the downward flow of the descending sap, which will be therefore forced to accumulate in the situation described. The reader may perceive that the origin from whence these two kinds of sap are derived, their chemical composition, the part of the vegetable through which they pass, the causes which produce the ascent of one and the descent of the other, together with the uses of both in the vegetable economy, are questions of great interest, as well to the farmer as the horticulturist.
The source from whence the ascending sap is derived is the aliment absorbed by the roots from the soil. This aliment consists essentially of two substances; one of these being sufficiently familiar, namely, water; and the other commonly existing in the atmosphere under the form of gas or air, but likewise capable of solution in water, namely, carbonic acid; this substance is known to every one as the cause, by its escape, of the boiling appearance seen in freshly uncorked soda water. Those two substances constitute the necessary aliment of vegetables: at the same time it is notorious that various matters, such as manures, earths, &c., greatly facilitate the growth of plants; but these matters produce this effect either by supplying a greater quantity of carbonic acid, or by acting in a manner similar to condiments; for in the same way as spices taken into the stomach along with food invigorate the digestive power, so do many minerals, when absorbed by the roots, operate in promoting the nutrition of vegetables.
The chemical composition of the ascending sap is chiefly a solution of sugar and gum in water. In the northern states of America, sugar in large quantities is obtained from some species of maple, principally the sugar maple and swamp maple of Canada, by boring the stem, collecting the ascending sap which flows from the wound, and evaporating away its watery portions. It is an interesting question, from whence proceed the sugar and gum contained in this ascending sap? The only satisfactory reply to this question is, that these substances become formed out of the water and carbonic acid absorbed from the soil; but this is a transformation which cannot be effected by the most expert chemist, so that we find in this, as in many other instances, a living body is a laboratory in which Nature executes changes far transcending the loftiest efforts of man’s ingenuity.
The part of the vegetable through which the sap ascends can be easily shown in any of the ordinary trees of this country. If a branch from a currant shrub be placed with its inferior and newly cut surface immersed at first in a solution of green vitriol and afterwards in an infusion of nutgalls, the course through which these fluids ascend may be traced by the black colour produced by their mixture; for every one knows that a mixture of green vitriol and nutgalls produces ink, and in the experiment just described, the solutions of these substances following each other in their ascent, inscribe in a manner on the interior of the branch the path which they successively pursued. This course will be found to exist between the bark and the pith, these parts being quite unchanged, while the intermediate portion of wood will be deeply coloured.
The causes which produce the ascent of the sap are of a very powerful nature. The celebrated Hales ascertained that a vine branch, in a few days, sucked up water with a force equal to the weight of sixteen pounds on the square inch: this was a power greater than atmospheric pressure; and when it is recollected that the pressure of the atmosphere is capable of lifting thirty-three or thirty-four feet of water in a common pump, some estimate may be formed of the force with which the sap ascends. This ascent appears to be produced by the influence of two causes: the one, a quality peculiar to living beings, by which the buds in common with all growing organs are capable of attracting or sucking towards them the juices necessary for their nutrition; and in agreement with this, the sap is found to ascend in the first instance near the buds: the other, a general property of all matter which has been but lately discovered. This latter property, which has been called endosmose, is found to operate when two fluids of different densities are separated by a membrane. Under these circumstances, and in obedience to an attraction for each other, both fluids pass through the membrane, and mix together; but the denser and thicker fluid finding a greater difficulty to penetrate the membrane than the lighter and thinner, consequently passes through in less quantity. To illustrate this, let us suppose a bladder containing a little syrup, and placed in a vessel of water, and we will have the conditions necessary for endosmose: the syrup and water will both pass through the bladder in opposite directions, but a greater quantity of water will pass into the syrup, than of the latter into the water. It will be evident to the reader that this excess of thin liquid passing into the denser will constitute a force or power which will require an equal force to neutralise it; and it has been ascertained that the tendency of water to penetrate a membrane for the purpose of mixing with a syrup of once and a third its own specific weight, required a force equal to sixty-three pounds on the square inch to overcome it. Now, a plant growing in the ground is similarly circumstanced to the bladder in this experiment: its roots furnished with extremities of spongy membrane are interposed between thin water and carbonic acid externally, and a syrupy solution of sugar and gum internally. Now, under those circumstances we need not be surprised if an endosmose should operate, abundantly sufficient to elevate the sap with a force even greater than that determined by Hales.
The use of the ascending sap in the vegetable economy is the last subject which we shall consider in this article. On a future occasion we shall endeavour to show that it is out of the ascending sap that the descending or elaborated sap is chiefly formed; but besides this utility of the ascending sap, as the source of the descending sap, the former has special functions of its own to perform. If we inquire what period of the year is the ascending sap in greatest quantity, we shall find it to be during the spring season. Now, this is the time when the buds become pushed out into branches, and the young leaves peep forth: the roots also during this season increase in thickness. Another means which we possess of ascertaining the uses of this sap, is by protecting plants from the influence of light: in total darkness no elaborated sap is ever formed; therefore, whatever vegetation may then take place, must be solely at the expense of the ascending sap. Under such circumstances the plant becomes very succulent, its stems grow to a great length, no vegetable fibre can be detected in its substance, its colour is blanched, it possesses no bitter or aromatic properties, and it does not develope flowers. Potatoes growing in a dark cellar, or celery protected from the light, by earth heaped around its foot-stalks, will afford familiar examples. These considerations lead us to the belief that out of the ascending sap is formed the fleshy part of vegetables, which, by its production, increases the length of the stem, and the thickness of the roots. In our next article we will describe the most remarkable properties of the ascending sap.