Shoot tips of ivy and some other vines are negatively phototropic,
meaning the shoot tips grow away from the light source or toward darker
areas. That allows the vine to climb solid objects. Most shoots are
positively phototropic so they would grow away from solid object rather
than climb them. I once saw an ivy grow into a dark basement through a
crack in the foundation. There was a window in the basement, but the
shoot continued to grow away from the window to the darker area of the
basement.

It may be that the opening in the fan simply allows the vine to grow
away from the light source due to its negative phototropism.

David R. Hershey


n cook wrote:
I have ivy that climbs up the wall, over the kitchen window sill, and up the
glass until I cut it back. All fronds grow vertically ove rthe glass except
those within a foot or so of being under an extractor fan mounted in the
glass and used daily. Those fronds grow unerringly directly, diagonally,
towards the extractor.
What evolutionary reason is there for ivy to grow towards a source of
vibration ?
Its the same every year, not some random quirk.