FIELD STUDIES OF CEREAL LEAF GROWTH .1. INITIATION AND EXPANSION IN RELATION TO TEMPERATURE AND ONTOGENY

Measurements of leaf initiation, appearance, and expansion are presented for winter wheat and spring barley crops. For winter wheat, these processes occurred during periods of several weeks when fluctuating temperatures influenced process rates. Analysis of these measurements was facilitated by plotting variables against the time integral of temperature above an appropriate base temperature (O °C), here called thermal time with units of °C d. Leaf primordial number and appearance stage increased linearly with thermal time for both winter wheat and spring barley which initiated 12 and 9 leaves respectively. When plotted against thermal time 90% of laminar and leaf length growth and 80% of laminar width growth was satisfactorily described by a straight line for both species. This enabled an average extension rate and duration of linear growth to be defined for each leaf. When expressed in thermal time, wheat leaves had a similar duration of linear growth (210 °C d; s.d. 30 °C d) with insolation exerting a negligible influence. The first seven barley leaves had a shorter duration of linear growth (151 °C d; s.d. 8 °C d). For wheat, final leaf length and laminar width increased with leaf number and were not apparently associated with changes in apical development stage. Changes of barley leaf dimensions with leaf number were more complex. © 1979 Oxford University Press.