Jorge, there seems to be ongoing debate about the mechanism generating positive pressure in sugar maple stems. One idea is the osmotic theory, as explained by Tim Howard, which invokes the involvement of living cells and sucrose to generate an osmotic pressure difference between fibers and vessels, which are assumed to be separated by an osmotic barrier (Cirelli et al. 2008). The classical view is that pressure development results from a purely physical mechanism, beginning with compressed gas bubbles that form in tiny air spaces inside branches (Ceseri & Stockie 2012) when they freeze.
--Seth Cirelli D, Jagels R, Tyree MT (2008) Toward an improved model of maple sap exudation: the location and role of osmotic barriers in sugar maple, butternut and white birch. Tree Physiology 28:1145-1155 Ceseri M, Stockie JM (2012) A mathematical model of sap exudation in maple trees governed by ice melting, gas dissolution and osmosis. SIAM Journal on Applied Mathematics 73:649 -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[email protected]] On Behalf Of Jorge A. Santiago-Blay Sent: Sunday, February 23, 2014 9:00 PM To: [email protected] Subject: [ECOLOG-L] maple sap question Dear Ecolog-Listers: Basic botany question. All along I have understood that the so-called "sap" from which maple syrup is manufactured comes products transported in the xylem. Thus, the liquid is harvested as it travels upwards from the roots into the shoot as the plants begins to increase its metabolic demands late winter and early spring. Because their contents are so diluted, they needs to be boiled extensively. The link below seem to suggest that the some people in the maple syrup industry believe that the sap is flowing down (I suppose on the direction of the roots). http://www.npr.org/blogs/thesalt/2014/02/02/270204651/sap-discovery-could-tu rn-syrup-making-upside-down Could someone let me know the: 1. anatomical vascular tissue through which the maple sap travels? This link appears to indicate it is sapwood, in other words, xylem, http://maple.dnr.cornell.edu/produc/sapflow.htm 2. direction of travel? The same site says, roots up, http://maple.dnr.cornell.edu/produc/sapflow.htm Thus, how can the link below appear to indicate other wise? http://www.npr.org/blogs/thesalt/2014/02/02/270204651/sap-discovery-could-tu rn-syrup-making-upside-down Gracias, sincerely, Jorge Jorge A. Santiago-Blay, PhD blaypublishers.com http://blayjorge.wordpress.com/ http://paleobiology.si.edu/staff/individuals/santiagoblay.html
