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Leafhoppers and many other insects feed off plant sap

Sap is a fluid transported in xylem cells (tracheids or vessel elements) or phloem sieve tube elements of a plant. Fluid found in the vacuole of other cells is sometimes referred to as "cell sap". Other liquid compounds found in plants or exuded by plants, such as latex, resins, and mucilage are sometimes incorrectly referred to as sap.

Xylem sap consists primarily of water, with hormones, mineral elements, and other nutrients dissolved in the sap. Transport of sap in xylem is generally "basipetal", or upward from the roots toward the leaves. Over the past century, there has been some controversy regarding the mechanism of xylem sap transport, although most plant scientists today agree that the bulk of the evidence supports the cohesion-tension theory of xylem sap transport.

Phloem sap consists primarily of water, with sugars, hormones, and mineral elements dissolved in the sap. Phloem sap transport occurs from sources (a location where carbohydrates are produced or stored) toward sinks (a location where carbohydrates are utilized). The pressure flow hypothesis proposes a mechanism for phloem sap transport.

Maple syrup is made from reduced maple tree xylem sap. In some countries (e.g., Russia or Latvia) it is common to collect the early spring sap of birch trees (so called "birch juice") for human consumption; the sap can be used fresh or fermented. "Birch juice" is slightly sweet and very refreshing, but tends to become bitter in late spring; the rule of thumb is to collect it before any green leaves have appeared.

See also

Wikimedia Commons has media related to:

Plant sap

• Latex
• Resin

References

• Angeles, G., B.J. Bond, J.S. Boyer, T.J. Brodribb, J.R. Brooks, M.J. Burns, J.M. Cavender-Bares, M.J. Clearwater, H. Cochard, J.P. Comstock, S.D. Davis, J.-C. Domec, L.A. Donovan, F.W. Ewers, B.L. Gartner, U.G. Hacke, T.M. Hinckley, N.M. Holbrook, H.G. Jones, K.L. Kavanagh, B.E. Law, J. Lopez-Portillo, C. Lovisolo, T.A. Martin, J. Martinez-Vilalta, S. Mayr, F.C. Meinzer, P.J. Melcher, M. Mencuccini, S.S. Mulkey, A. Nardini, H. Neufeld, J.B. Passioura, W.T. Pockman, R.B. Pratt, S. Rambal, H. Richter, L. Sack, S. Salleo, A. Schubert, P.J. Schulte, J.P. Sparks, J.S. Sperry, R.O. Teskey, and M.T. Tyree. 2004. The cohesion-tension theory. New Phytologist 163:451-452.
• Raven, P.H., Evert, R.F. and Eichhorn, S.E. 1999. Biology of Plants. W.H. Freeman.
• Taiz, L. and Zeiger, E. 1998. Plant Physiology. Sinauer Associates, Sunderland, Mass.

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