Quote (Dorothy Potter Barnett): >Would you please also address the reason for the sugar found >externally on orchid leaves, stems, flowers...? I've heard it is >excess fertilizer, but would like to know more.
What sugar is that? I would suggest two sources: aphids and, perhaps, guttation. Many aphids and other sucking insects such as scales emit honeydew to reward the ants which tend and defend them. If you have parked your car under a lime tree in summer, you will know the result: a sticky goo, contaminated with fungi. Guttation is the phenomenon that one sees at dawn - as distinct from dew - whereby grasses - in particular - exude drops of water from their leaf tips and axils - where the leaf and stem join. It is not known why this happens - as it represents a major loss for the plant - but it is thought to be an osmotic overshoot, when plants break down stored starch into sugar in order to grow, but the temperature proves to be too low for these to be taken up by the metabolism. The osmotic suction that this places on the roots draws water into the leaf cells, which have to excrete it if they are not to burst. They do this by shipping out ions and sugars, which in turn draw out the excess water. This is very wasteful, however, and leaves the plant prone to rots. ______________________________ Oliver Sparrow _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
