Plants constitute over 90% of the world's present and past biomass. Simply in terms of their bulk, whatever we learn about plants has the potential to tip the balance in any debate concerning the frequency of occurrence of a biological phenomenon. From the archaic algae to the most derived and evolved multi-cellular terrestrial plants, from the spectral properties of the light-harvesting pigments in the chloroplast to the stacking of leaves in the tree canopy, we are persistently drawn to the conclusion that behaviour of plants is in large part responsive to and intimately connected with the way the physical environment operates and is constructed. From their shape and size, we can reconstruct much of the ontogeny and development of its species, we can determine the potential for long distance dispersal and reproductive biology of species. Finally, throughout their billon-year history, we can infer a metabolic dependency of plants' vegetative growth and survival on the availability of light, water, minerals and space.
Nowhere else in biology than in plants do we find such convincing evidence that physical laws and processes link form and function and thus have confined the scope of organic expression within the boundaries that have never been breached. The task of the plant physiologist thus is to identify theses limitations and, at a finer level of analysis, demonstrate how physical principles have demonstrably influenced the morphological, anatomical, physiological and biochemical directions taken by individual plant lineages during the course of their evolution.