In case of a tree tapped on both the north and south sides at the same level, it was found that the north spout yielded daily about twice as much sap as the south, and continued to flow nearly two weeks longer. To discover whether the sweetness of the sap was the same in all parts of the same tree, spouts were inserted in a tree which had never previously been tapped—one at the usual height, one fifty feet higher, where the trunk was about five inches in diameter, and a limb thirty-five feet from the ground was cut. In several hours the lower spout yielded six pounds of sap, the limb two ounces, and the upper spout none at all. Similar experiments of other trees showed the flows of sap to be most free within twelve feet of the earth, dinunishing rapidly above that height. Experiments upon the roots proved that the sap flowed from both ends of a cut root, and that it all contained sugar.
The largest flow noticed during any one spring day was from a healthy shade-tree, six feet five inches in circumference, March 23, and amounted to ten pounds and three ounces. Sap gathered from the latter tree November 7 was found to contain only half as much sugar as that obtained in March from the first tree. Mr. Hubbard, an experienced sugar-maker, is of the opinion that the amount of sugar obtained from a single tree cannot be augmented much by multiplying the number of spouts.
Two half-inch holes about two inches deep suffice for ordinary trees, while four spouts and two buckets are used for very large trees. The average annual product of the sugar maple varies from twelve to twenty-four gallons of sap, yielding from two to three pounds of sugar, though the yield of a single tree is said to have exceeded thirty pounds in one season.
Birches seem to exceed all other trees in the amount of sap which they yield—black, yellow, paper, and gray or white birch were tested and reached the maximum of fifteen pounds per day per spout. They were tapped March 19, commenced yielding on the 25th, and ended the last of April.
At six o'clock, a.m., April 2, the two gauges in a black birch—the first at the ground and the second thirty feet higher up—indicated respectively pressures of 56.65 and 26.74 feet of water, the difference corresponding almost exactly to the difference in height. A hole being bored at 12.30 p.m. opposite the lower gauge, the pressure fell in fifteen minutes equal to 10.27 feet of water. Upon closing the hole the pressure rose to its former level in ten minutes. A stop-cock having been inserted into the hole, it was found that the communication between it and each of the two gauges was almost instantaneous; proving that the tree was entirely filled with sap and exerted its pressure freely in all directions. This sap-pressure continued to increase until May 11, when it represented a column of water 84.77 feet high—probably the highest pressure of sap ever before recorded. This pressure gradually decreased until May 27, when the lower gauge indicated zero. The suction manifested by the birch was very httle, never exceeding nine feet of water, and continued for but a few days.
To determine whether this pressure was due to the vital action of the roots alone, a root was followed for a distance of ten feet from the tree, and then, one foot below the surface, cut off. To this detached root, one inch in diameter, a gauge was attached, April 26. The pressure became immediately evident, and rose, with slight fluctuations, until noon of April 30, when it indicated a column of water 85.80 feet high. The original experiment of applying a gauge to the grape-vine, first tried by Rev. Stephen Hales, of England, one hundred and fifty years ago, was now repeated, May 9, and on the 24th showed a pressure of 49.52 feet of water— six and a half more than was observed by Hales.
The peculiar features of the vine-sap are its lateness in the season, its apparent independence of the weather, its moderate and uniform rise to its maximum, its gradual dechne to zero without marked fluctuations, and its almost unvarying suction of from 4.5 to 6.5 feet of water between June 20 and-July 20, -when the observations ceased.
The general indications of the mercurial gauge seem to show that the flow of sap is caused by the absorbent power of the roots forcing water into the tree, and as, even in the maple, the sap rarely rises more than twenty feet from the ground, and the development of leaf and flower buds is not usually affected by any mechanical pressure of the sap forced into them from below, their vitality is stimulated to activity by the genial influence of the sun, and their growth is, in its beginning, caused by the assimilation of organic substances accumulated during the preceding season of vegetation.
These experiments and observations are not final and conclusive in several respects, but they may be looked upon as having opened the door to an almost exhaust-less subject of which the world needs information. I hope they will be read with interest by the most indifferent, and will be carefully studied in all their relations to the natural world by those who delight in such researches.