cane, the proportion of saccharine and mucilaginous matter to the water is about as one to five. In the sugar maple it is about one to forty of the whole. In the beech, according M. Vauquelin, it is about one to forty-two; and in the elm, one to eighty-eight.

Mr. DAVY mentioned the relation of the different kinds of sap in trees, to the subject of engrafting. Grafts from fruit trees containing a saccharine sap, sap, will not grow on trees, the sap of which is in the slightest degree astringent. In this part of the enquiry, Mr. Knight's observations upon the decay of grafts taken from old trees were made a topic of discussion, and it appeared probable from the facts, that the graft partakes of the disposition to old age, and decay of the parent tree; and that though it does not die at the same time by any Talicotian sympathy, yet it cannot by any means be made healthy and vigorous. All the favourite apples of the last century are gradually deteriorating. The golden pippin has not a fourth of the size described by

the old writers on gardening; and our hopes for new and excellent varieties must rest upon enlightened experiments on seedlings.

IN the fourth lecture the peculiar fluids, or, as they have been called by some physiologists, the secreted fluids, of plants were considered.

THE Vessels in which they are contained seemed to be cylindrical, and of the largest size belonging to the vegetable system, and distributed through the alburnum as well as the bark.

THE resinous, oily and aromatic matters found in plants are all probably contained in those vessels.

Mr. DAVY pointed out some of the obvious uses of the secreted fluids, both for nourishing and conserving the parts. In seeds, the oily constituent which preserves them through the winter, becomes in the spring a part of the food of the plume and radicle. The aroma belonging to flowers, seems intended to preserve the essential, the reproductive parts, from attacks of insects, to which the volatile

oils appear to be peculiarly offensive, and even destructive. Multitudes of aphides are often seen upon the calyx of the rose, but they never dare to attack the petals, and there are many analogous instances.

The fifth lecture was principally devoted to the examination of the causes which influence the motion of the sap. The sap rises through the tubes of the alburnum, is modified in the caves, and seems to descend in the bark. Mr. Davy is inclined to refer this motion to physical causes chiefly. To capillary attraction, to expansions and contractions of the vessels, from changes of temperature, and to the great evaporation from the leaves.

He seemed to doubt of the presence of irritable contractile power in the fibres of vegetables, and shewed that the other agents were adequate to the effect.; He decided against the idea of any circulation in the vegetable system, similar to that occurring in the animal system, in which the heart and arteries are inva

riably active. And he detailed several instances of the inversion of the functions of the vessels, by merely changing the mode of application of external powers.

IN the sixth lecture, water, soils, and the atmosphere, were considered, as far as they are connected with the nourishment of plants. Water and the matters in the soil which have once been organized, constitute the great part of their food received by the roots. Mr. Davy detailed the experiments of T. de Saussure, which prove that the earths found in the ashes of plants, is of the same kind as the earths of the soil in which they grow. He mentioned an original experiment, which seemed to shew that corn would not grow vigorously if wholly deprived of silicious earth, which, in the state of nature, constitutes its epidermis, and it has no power of forming this substance, which there is good reason for supposing elementary.-Mr. Davy gave an account of the experiments which shew that carbonic acid is absorbed and

decomposed by plants in the solar light and oxygen evolved. He seemed inclined to doubt whether they ever evolved carbonic acid in a state of health; and he mentioned some facts, which seemed to shew, that the carbonic acid which usually appears when plants are confined in darkness, in close vessels, is really owing to the decay of some of their dead parts. The epidermis, the heart wood or a single yellow spot in the leaf, would be fully adequate.to such an effect.

THE seventh lecture was principally devoted to the consideration of the causes of germination and the circumstances that affect the health of plants. Mr. D. stated that seeds were incapable of germinating, unless supplied with heat, moisture, and air, and that oxygen is always absorbed in this process, and carbonic acid evolved. He mentioned Mr. Knight's experiments on the ascent of the stalk, and descent of the radicle, which seem to shew that gravitation is the principal cause of both these effects.