Maple sap

James W. Perry jperry at UWC.EDU
Tue Mar 11 16:58:18 EST 1997

At 12:51 PM 3/11/97 -0800, you wrote:
>Dear Plant edders,
>I have a question concerning collecting sap from maples for the making of 
>maple syurp.  Why doesn't the phloem plug up due to callose and p-protein 
>when a tree is tapped to collect sap?  This normally happens in other 
>plants doesn't it?  Am I missing something here?  Can anyone help answer 
>Dave Haas

Indeed, something has been missed. Maple sap is collected from the sapwood,
not from the phloem tissue! The tap is driven in well past the phloem, into
the sapwood. 

The mechanism of flow is still poorly understood to the best of my
knowledge, but what's being withdrawn are sugars (sucrose) and minerals that
have been stored within xylem parenchyma cell over the winter, and which are
now being mobilized in preparation for renewed growth.

Jim Perry

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