Composition of plant sap

1061. The sap undergoes important changes in its progress through the plant. When first taken up by the roots, it should contain carbonic acid, ammonia, water, and some kind of mineral substance; the latter, though found in very small proportions, being quite essential to the health and vigour of the plant. As the sap is diffused through the plant, the carbonic acid, ammonia, and water which it contains, are decomposed, and their elements are separated, to form afterwards, by new combinations, wood, starch, sugar, gum, and other vegetable products.