In Chenopodium rubrum there is a multiplicity of rhythmic phenomena with different circadian periodicities in the different plant organs (leaves, shoot, apex), which under synchronizing light/dark or low/high temperature cycles will coexist with specific phase relationships. The different organ systems most likely display their periodic organization in electrochemical oscillations, which could be the basis for communication between the tissues via frequency coded signals. The perception of a flower inducing dark period possibly leads to a change in the electro-chemical signalling between leaves and the apex to allow flower initiation to occur. The involvement of action potentials is anticipated, which might trigger cytoplasmic changes in pH or Ca²⁺ as secondary messengers in the photoperiodic signal transduction. There is evidence that systemic responses of plants might depend on electrochemical hydraulic controls operating at the level of membranes. Turgor dependent volume changes, stretch-activated membrane channels and correlated changes in membrane potential might be an essential part of the "hardware" for signal transduction at the cellular and organismic level. The "software" could involve frequency-coded signals at the cellular, the tissue and the organismic level. To elucidate the communication between plant organs via action potentials will be most rewarding. It certainly will be a great challenge to induce flowering (or other systemic reponses) by frequency-coded electric stimulation.