On the question of sugary exudates external to the orchid flower, I have
always assumed they function to attract ants to the orchid plant and/or
flower. The ants, in turn, would then protect the orchid from herbivorous
insects. (I believe a similar situation can be found in the peony.)
Considering the intimate relationships found between ants and other tropical
plants, this would be a natural extension. Although guttation is associated
with reducing fluid pressure and does contain water and minerals, I find it
difficult to believe that orchids are in a position to "fritter away" excess
sugar.
Close examination of certain orchids (Cymbidiums come to mind) will reveal glands at the base of flowers and sometimes on other parts of the plants. These are the locations of the thick sweet substance to which reference has been made in previous postings. This is not guttation as several have suggested, but clearly an extrafloral attractant produced at specific locations. I believe (but have no empirical evidence or paper to cite), that in habitat this would encourage ants to protect the inflorescence from predation.
Dennis Westler
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