Roots in medium vs outside of pot: are they all air roots?

[karrolhk]

There seem to be different types of roots in an orchid:
1. roots in traditional medium (bark and moss)
2. roots in water culture medium (just water)
3. roots that grow outside the pot

Are they the same: i.e. all air roots? Do #1 and #2 have velamen like the air roots? I have read that #3 have velamen but they won't be able to absorb water when put in the medium.

Or, are they different? How are they different? because #2 is adapted to growing in water, what makes #2 different from #1 to be adapted to growing in water? If they are different, do they have different names?

Thanks