are full grown, and when the annual shoots have ceased to elongatel
than at any earlier period. This energy in the powers of vegetation
must certainly, Mr. Knight thinks, be employed in some very im-
portant operation. He has observed that the produce of his meadows
has been greatly increased when the herbage of the preceding year
had been left till the end of autumn, on ground that had been mowed
early in the summer; from which he has been led to imagine, that
leaves are employed during the latter part of the summer in the pre-'
paration of matter calculated to afford food to the buds and blossoms
of the succeeding spring.
In order to determine whether the foregoing opinions were well founded or not, Mr. Knight made the following experiments.
Having made incisions in the trunks of sycamore and birch-trees (some of these incisions being close to the ground, others at the ele- vation of seven feet), he found that the sap obtained from the syca- more close to the ground, was of the specific gravity of 1004, while that obtained at the height of seven feet had a specific gravity of 1008. The sap of the birch was somewhat lighter; but the increase of spe- cific gravity, at different elevations, was comparatively the same. The sap of both these trees, when extracted near the ground, was almost void of taste ; but when obtained at a greater height, it was sensibly sweet. In one instance it was extracted from the sycamore-tree at the height of twelve feet; it was then very sweet, and its specific gravity was 1012.
Mr. Knight then made an experiment to compare the sap obtained from a recent incision with that obtained from an old one. He found that the sap from an old incision was reduced in specific gravity to 1-002, while that from the recent incision continued at 1-004, as before. These incisions were made in a sycamore-tree, and were close to the ground.
Some observations then follow on the variation in the specific gra- vity of the albumum at different seasons. After taking every pre- caution to avoid error, the author found the specific gravity of winter- felled oak to be 0679, and that of summer-felled oak to be 0609, after they had both been immersed five minutes in water. This dif- ference appearing to Mr. Knight very considerable, he repeated the experiment several times, but found no reason to suspect any error in it; and upon measuring pieces of both kinds of wood, which were equal in weight, it appeared that the winter-felled pieces were much less than the others. The more recently formed layers of winter- felled wood had a specific gravity of 0-583 ; that of the summer-felled wood was only 0533. In another experiment the former was 0588, the latter 0534.
On pouring boiling water on equal quantities of summer- and of winter-felled wood, it appeared that the latter communicated a much deeper colour to the water than the former; it also raised the spe- cific gravity of the water to 1002 ; the specific gravity of the other infusion was 1-001.
Mr. Knight thought he had reason to believe that the matter de-
