a fluid secreted from the cut vessels of the wood of stems or roots of living plants. The secretion, which is caused by root pressure, is sometimes called the weeping of plants. Sap exudates contains mineral salts and some organic substances, mainly amino acids, sugars, and proteins. The exudate characterizes both trees and herbaceous plants. The quantity secreted by some tree species during a vegetative period is from 50 to 150 l. Herbaceous plants, such as pumpkin, yield 4 to 5 l.
Sap exudate is most abundant in early spring owing to the transport of nutrient matter to budding leaves. During this period, its sugar content reaches 3 to 8 percent. Because the fluid is rich in nutrient matter, it is obtained from some trees, such as the sugar maple or birch, for use as a beverage or as an ingredient for the production of maple sugar. To collect the sap exudate, the trunk is cut or drilled to the young wood. This procedure does not damage the tree.