On Thu, 6 Dec 2007 20:28:07 -0800 (PST), Frank
wrote:

Jar holding cuttings in water is starting to develop a
green film, likely fed by the weak plant food solution.

Since algae liberate oxygen, and oxygen stimulates
rooting, which is desired, is the algae in this case
beneficial?

Not sure. Algae growth can support a host of micro-organisms, both
good and bad. I rinse out my cutting container and remove any
decaying debris weekly. Most roots prefer a dark environment.