White Spots On Stem Base?(Diagram Inside)

Doin closet hydro, plants thriving, no signs of bugs eating leaves. Just seen these white spots on stem base and gradually moving upward. Both plants are in same res, and same spots on both in same areas. Wut could it b? Heres sumthin i drew up below..since cant upload pics from cam fora while:
http://i224.photobucket.com/albums/d...antproblem.jpg

Are they just spots, or are they little bumps or nubs?
Air-rooting is very very common in humid environments and I see it in hydro far more often than in soil.
Do the plants look healthy otherwise?
Is your ambient humidity over 50%?