Re: Aquatic Plants Digest V1 #342

Frank you wrote

> Subject: Re: adjusting daylength (to flower horemanii)
> For anyone who has experimented with artificial light to change daylength in
> order to flower plants (as per discussion for E. horemanii), how important
> is the annual cycle?
 This is entirely species and genus specific
> - - When a short day (e.g. 8-hours) is needed for flowering, is a
> complementary long day followed by transition periods needed?

No it is only the night length that is important. Some plants require 
only a single long or short day to initiate flowering and some require a 
defined period of time at that day length. It also may be linked to 
temperture as well. Some plants will also not flower unless both the day 
length and the temp are in the correct range. Also you need to watch out 
for lights switched on during the night a few minutes can destroy the 
long night. So if you do this no peeking at the tanks late at night after 
the programmed lights have gone out.

> - - Or, can a short day immediately follow a 12-hour day?
A species of grass that is used here for research only requires a single 
day to initiate flowering (very handy for them to find genes specificaly 
up regulated upon flowering initiation)
> - - In either case, for how many weeks is the short day needed to trigger the
> response?
 Probably less than a week below the critical level, I can't answer that 
one for sure. Eight hours should be sufficient and if that is held for a 
week that should also do for a starting point.
> - - And what about concomittant changes in temperature, light intensity, etc 
temp see above, light intensity is probably not so important because it 
is naturally variable depending upon the specific micro environment of a 
single plant.

Peter Hughes