The length of the extension zone (LEZ) of emerging wheat leaves varied with the stage of leaf development and between leaves with the length of the encircling sheath (LES). The ratio LEZ/LES varied from 0·60 when the leaf tip emerged from the encircling sheath to 0·35 when the ligule emerged. The relationship between LEZ/LES and an index of leaf development (DI), defined as the sheath length of the growing leaf relative to LES, was: LEZ/LES= 0·632 exp (-0.622.DI); (r= 0.91). 14C incorporation studies supported the measurement of extension zone location and length.
There appeared to be a small zone of non-expanding tissue, within the extension zone, around the ligule, but it was not a major discontinuity within the whole extension zone. The relative extension rate of the extension zone declined by only 50 % from leaf tip to ligule emergence whereas the relative extension rate of the whole leaf declined by 90 % over the same interval.
There was little variation in protein and carbohydrate concentrations around the upper limit of the extension zone in emerging leaves. For studies of leaf growth in wheat where it is not possible to measure LEZ, harvesting the lower 50 % of the enclosed part of an emerging leaf would adequately sample the extension zone.