My understanding parallels Ted, partially for the reasons King mentioned - orchids have limited stomata compared to most terrestrial orchids, they tend to be more highly concentrated on the bottoms of the leaves, and in many plant - notable phals - the stomata are closed in the daytime.
Add to that the waxy coating on the leaves to reduce transpiration, and it seems more likely (to me anyway), that foliar feeding is effective, as the liquid drips off the leaves into the medium!
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