Photosynthesis in the Ears of Five Varieties of Wheat

Abstract

IN view of the observations of Knowles and Watkin¹, and of Watson and Norman², working with wheat and barley respectively, that about one-third of the final dry weight of the plant is added during the post-ear emergence period, the assimilation by the plant during this period merits special consideration as a factor in determining final yield. The concept of the net assimilation-rate, as originally proposed by Gregory³, and so successfully used by him and others^4–6 in interpreting problems of crop-growth, would thus appear to require reconsideration, since the net assimilation-rate is usually estimated up to the stage of maximum leaf-growth. After this stage the proportion of green-leaf surface to that of other green parts diminishes appreciably with time, and the assimilation by the latter might be expected to contribute substantially to ultimate dry matter output. In fact, Boonstra⁷, Smith⁸, Watson and Norman² and Archbold⁹ found that, in cereals, assimilation by the stems and by the ears themselves contribute substantially to grain yield.