Regarding the root collar: plants in the Phalaenopsis subgenus Esmeralda do
this. It is one of this group's odd autopomorphies. Unlike other Phals in
other sections of the genus, this group will produce a principle push of
roots out of the stem in a collar all the way around the plant. Eric
Christenson says in his book that (being terrestrial rather than epiphytic,)
"this is presumably an adaptation to rooting in and rising above a fresh
layer of leaf litter in nature".

I don't know if I can connect the dieing lower leaves to this root
production the way you have. First, when it happens to my plants in this
group, leaves do not necessarily die as a result. Most often, the roots
either push out and through the tissue or shove the leaves out of the way
and come out from behind them. Because leaves are dying at the same time
does not mean there is a relationship between the two observations or, if
there is, that it works the way it first appears to. Maybe the older leaves
began the process of abscission and in so doing produced chemicals that
triggered the root growth rather than the other way around.

"OrchidKitty" wrote in message
oups.com...
This morning while watering the herd, I noticed that my doritis are
sending out A LOT of aerial roots, and the the roots are punching
through the leaves or bending the leaves so they will be forced to fall
off. For instance, my Doritis buyssoniana, a very large plant, has
seven pairs of leaves, and the bottom five pairs are being disturbed or
destroyed by roots erupting from the "stem" of the plant. (The "stem"
is a good seven inches in length from roots to crown.) Similarly, the
Doritis pulcherrimas, which are a much smaller species, are all having
the same problem. Other than this self-destructive behavior, the plants
look healthy. Am I doing something wrong? Is this natural behavior?
The plants are growing in a sunroom--either in natural light or
flourescent light; the humdity ranges from 60% to nearly 80%; some
plants are in S/H and others are in bark.