Influence of Tops and Roots on Net Assimilation Rate of Sugar-beet and Spinach Beet and Grafts between them

Sugar-beet has a larger storage root and greater net assimilation rate (E) than spinach beet. To determine whether the greater root was a result or cause of the greater E, grafts were made between tops and roots of sugar-beet and spinach-beet in all four possible combinations. Grafted plants with sugar-beet roots had greater E and root dry weight, less leaf area and top dry weight and lower concentration of sugar in the leaf lamina, than those with spinach-beet roots, irrespective of the type of top. Grafted plants with sugar-beet tops had greater E, total and root dry weight, but less leaf area, than those with spinach-beet tops, irrespective of the type of root. The difference in E between grafted plants with sugar-beet tops and spinach-beet tops was similar to that between grafted plants with sugar-beet roots and spinach-beet roots. It increased with time to 60 per cent. Increases in E probably represent increases in rate of photosynthesis. Sugar-beet roots probably increased photosynthesis by providing a better sink for assimilates than spinach-beet roots.