Experiments were made in 1936 and 1937 on barley plants grown in pot culture, to determine the effect of shading the ear or the shoot after ear emergence on dry weight and nitrogen content.

It was found that after ear emergence the ear and the shoot (leaves and stem) make approximately equal contributions to the assimilation of the whole plant. In the 1936 experiment 28% of the final dry weight of the ear was accounted for by assimilation in the ear itself, and in the 1937 experiment, 19%. These are minimum estimates, for assimilation must have been proceeding in the ears during emergence, before the shading treatments were applied. The results agree well with similar estimates of the extent of assimilation in the ear made on wheat by other workers.

The effects of shading on the amount of nitrogen present in the plant at harvest were somewhat variable, but they were always small compared with the effects on dry weight. Shading tended to reduce the amount of nitrogen in the ear, but as the dry weight of the ear was reduced to a much greater extent, - nitrogen as percentage of dry matter in the ear was increased. It is concluded from this result that translocation of nitrogen compounds to the ear is not closely dependent on the amount of the concurrent increase in dry weight of the ear. It appears that the approximate constancy of nitrogen percentage in the ear and the grain throughout development is a consequence of the particular conditions prevailing during normal growth in the field.

The experiments showed that 20–30 % of the dry weight of the whole plant was added after ear emergence, suggesting that climatic conditions during this late stage of growth is of considerable importance in determining the final yield.

The authors wish to thank Miss J. Hellyer for carrying out many of the determinations of nitrogen content, and Mr S. A. W. French for assistance with the statistical computation.