Unfortunately, that one quip in the NPR piece had it wrong; lets hope it was the editors or reporter and not the producers that had the misunderstanding. The sap flows up through the xylem in the spring. Cold temperatures in the winter causes sap in the tree to freeze, forming air bubbles and breaking the continuous stream of sap in the xylem (needed for transpiration in the summer). To remove these air bubbles, storage cells in the roots pump sugars in the xylem (via active transport), causing a strong diffusion gradient for water to move into the xylem. Water forcing its way into the xylem in the roots causes root pressure and subsequently forces the sap to rise up the stem of the tree (removing the air bubbles along the way). It's a nifty strategy to deal with cold climates and I expect is reflected in the more northerly distribution of this species (and birch, too, which also does this). Conifers have very different xylem cells, which can recover from frost embolism much more easily. Ring-porous species, on the other hand (ash, oak, hickory), cannot recover as thoroughly and must grow a new ring of xylem each spring before being fully operational. Cheers, Tim Howard New York Natural Heritage Program // SUNY ESF
>>> "Jorge A. Santiago-Blay" <[email protected]> 2/23/2014 9:00 PM >>> 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-turn-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-turn-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
