/ Osoi Eis Christon
D. Koubaroulis wrote:   In the old byzantine music book of Pandekti, 1851 (vol 4) the hymn
  "Osoi eis Xriston" (Those who have been baptised in Christ)  is
  mentioned as First Plagal mode. The only explanation I can give as to
  why it is not First mode (as it probably appears as in the new
  byzantine music books) is that the melody has a descending feeling.
  However, the endings in DI and the general melodic structure remind of
  fist mode rather than first Plagal. What is happening there?

Y. Bilalis wrote:

That is how it was referred in the old mss, but with diferent melodic
structure. Now in pandektis the name stayed but the structure is
probably new.