So action potentials may propogate more slowly in some plants - but there is probably evolutionary pressure for fast action potentials such as the ones found in the venus fly trap and others that have not been discovered yet. It is the opinion of the electrophysiologists at LINV that action potentials found in plants of 270m/s are anything but instrumention error however.
It is time to invest in a cheap usb dtat aquisition board and instrumentation amplifier - but which one ? I need to get the signal from the board to max msp . Plant > instrumentation amplifier > data aquisition board (DAQ) > MaxMSP
These guys have been really helpful : http://pleased-fp7.eu/?page_id=81