Sweaty trees?

[Tony Travis]

Marc Knight (Marc.Knight at uk.ac.ox.plants) wrote:
: Dear All,  I know I should know this (and probably did once) why why exactly 
: do trees 'sweat' in summer?  Also why does this 'sweat' contain sugars, isn't 
: that rather wasteful?

One explanation might be guttation caused by positive pressure in the
xylem under humid conditions but, since sugars are not normally found
in the xylem solution, I suspect you have observed 'leakage' from the
phloem through stylet holes left by aphids.  This often leaves a
sticky, sugary solution on the leaves of aphid infested plants/trees.

	Tony.
-- 
Dr. A.J.Travis,                       |  JANET: <ajt at uk.ac.sari.rri>
Rowett Research Institute,            |  other: <ajt at rri.sari.ac.uk>
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