What does propagates mean in this excerpt from T S poem Gerontion?

The line to which you refer is, "Thought has germinated and is now almost quiescent; it withdraws down the root, and nothing is known as `thought' any longer. The dove descending breaks the air with flame of incandescent terror; of bliss so overwhelming that she knows she is consumed, yet cannot cease to be, or cease to burn." The word, "propagates" does not appear in the excerpted lines, but its meaning is implied in the word, "germinated." As the dove descends, consuming and flaming, her bliss propagates, or spreads itself, across the landscape, enveloping all that it encompasses.