Bean leaf expansion in relation to temperature

When dwarf Phaseolus vulgaris plants were grown in a controlled environment at 20, 25, 30, and 35° C, expansion of the primary leaves occurred in two phases with an intermediate lag. Varying rates and duration of expansion were involved, leading to greatest final areas at the two intermediate temperatures. Dry weights of the leaves and leaf areas were similary influenced by temperature, except that the initial rates of increase continued for a longer period for weights than for areas. The rates of cell division and final numbers of cells were similar from 25 to 35° C, but both were decreased at 20° C. Final cell sizes were, on the other hand, decreased only at the highest temperature. The time trends of cell expansion varied greatly with temperature.Leaf expansion is discussed as a possible consequence of substrate supply, which may be determined by temperature in a number of ways. Cell division and cell expansion are not considered to be joint direct determinants of leaf expansion. Temperature influences division, with two consequences; the rate interacts with substrate supply to determine size of cells, and final cell number affects potential leaf area. Cell size is regarded as being secondary to numbers of cells and total material available, although some factors can vary cell size independently of substrate, e.g. water status.An important control of leaf growth, until the attainment of about half the final area, may be exercised by way of the leaf. Subsequently, intra-plant competition is likely to dominate