Lilium scales requiring material from the mother bulb's base plate
It's probable than anyone who has propagated lilies in large amounts has
observed
that scales do not produce bulblets only at the basal plate--in fact,
some bulblets
are often produced along the edge of the upper parts of the scale. In
one of the
older lily society yearbooks, there is an article describing an attempt
to produce
more bulblets by scoring or scratching lily scales. The result was a
great increase
in production of bulblets--but the bulblets produced were individually
much smaller.
The large amount of hand labor involved meant this method wasn't
feasible on a
commercial scale.
There are a lot of factors involved--vigorous lilies that produce
large scales are
more likely to produce large, vigorous bulblets. Easter lilies produce
bulblets
rapidly, and they grow vigorously and may flower the first year.
Western American
lilies with relatively narrow, thin scales, produce bulblets
reluctantly, and they grow
slowly. Timing that matches the lily growth cycle is a factor, so is
the temperature
at which the scales are incubated. Etc.
Ken