Mark said:
From your explanation, I assume that "weeping" trees have unique
hormone levels that cause branches to droop rather than grow upright.
So ... are weeping trees actually a third form of growth (apically
dominant, basally dominant, and weeping) ?

There are several mutations that cause "weeping"; and they seem to have
more to do with the plants's response to hormones rather than to
hormone levels themselves. I don't know what you mean by "basally
dominant"; all plants are apically dominant to different degrees.

And ... I ran across another "SuperThrive" like product called
"MegaGro" which claims to contain a substance called Potassium Gibberelate.

Gibberellin is a real plant hormone which has many various effects on
plants. There's a fungus that causes a disease of rice called "foolish
seedling disease" (probably sounds better in Japanese), making
seedlings grow tall and spindly. The fungus produces an artificial
gibberellin, changing the growth of the plant. Gibberellin is
sometimes sprayed on seedless grapes to make them bigger; on radish to
retard bolting; on fruit trees to increase fruit retention, etc. etc.
etc. It has its uses, but it's not miraculous. There's a product
called "Bonzi" (seriously) that makes ornamental plants more compact.

Nina