Abstract: Experiments were carried out with wheat plant in pot cultures to assess the contributions to grain material from assimilation by different organs during the ripening period and from reserve material in these organs, and to evaluate the amount of trans- located material between culms. The influence of soil moisture on these processes was also investigated. Twelve treatments (defoliation, deearing) were made as shown in Fig. 1. Only the main stem and the largest tiller were kept in each plant and subjected to these treatments at the time of ear emergence; the remaining tillers had been removed at an earlier stage. Two levels of soil moisture, namely 20% and 15% to soil dry weight, were maintained during the post-ear emergence period. The results may be summarized as follows. 1. The dry weight gained from current photosynthesis after ear emergence nearly equals to the dry weight of grains (Table 1). The substances lost from vegetative parts amount to no more than 10% of the grain weight if they were all translocated to the ear. Decrease of the carbohydrate supply to the ear by either defoliation or drought, or both, causes an increased drain on the reserve material in the vegetative parts, but the maximum amount does not exceed 1/3 of the grain weight. The translocated material comes mainly from the stem, its amount being determined primarily by the relative supply and demand. 2. The most important organ of dry matter production during the ripening period is the leaf-blades. The ear and the stem plus sheath make approximately equal contributions (Table 2). Under our experimental condition, the leaf-blades contribute about 2/3, and the ear and the stem plus sheath about 1/6 each to the total net assimilation. Difficiency of soil water leads to a considerable reduction in the assimilation by leaf-blades, while that of other organs is little affected (Table 5). 3. The removal of leaf-blades enhances the assimilatory activity of the remaining stem, sheath, and ear, indicating the existence of a compensatory reaction between the various green organs (Table 2). The amount compensated is, however, not large, being only about 1/5–1/3 of their original assimilation, and can make up only 1/10–2/10 of the loss due to defoliation. If there is another available source of material such as a leaf-bearing culm on the plant, no compensatory reaction can be observed. 4. The assimilation of the leaf and stem is markedly inhibited after the removal of the ear. The inhibition may amount to 80%–90% of their original assimilatory capacity. No inhibition is observed if there is a leafless culm on the plant. The absolute amount of inhibition is smaller when the assimilation of leaf-blades is low due to water shortage. 5. There is no translocation of assimilates under ordinary conditions between earbearing culms. Transport takes place only when there is a great difference in supply and demand between them. A defoliated culm can derive 1/2–3/4 of its grain weight from another intact culm (Tables 2, 5). 6. Removal of the aerial part of one culm at earing stage makes the remaining culm grow better than when both are present. Apparently the higher root/top ratio improves the water supply and the assimilatory activity (Tables 7, 8).