Short communication: thermal regimes in hollow stems of herbaceous plants-concepts and models.

Although there have been studies of the temperature regimes within flowers, micrometeorology within stems seems to have been overlooked. We present ideas, hypotheses, and a diagrammatic model on the biophysical and thermodynamic processes that interact in complex ways to result in elevated temperature regimes within hollow stems of herbaceous plants. We consider the effects of the ambient air around the stems, the possible importance of insolation, and greenhouse effects as influenced by stems' orientation and optical properties, i.e., reflection, absorption, emissivity, translucence, pigmentation, and thermal conductivity. We propose that greenhouse effects contribute significantly to and are influenced by the above phenomena as well as by the gross anatomy (volume:surface ratio; wall thickness), evapotranspiration, and the thermal properties of the gas mixture in the lumen. We provide examples of those elevated temperatures that can be several degrees Celsius above the temperature of the surrounding atmosphere.