The effects of boron deficiency on certain components of cells was followed by tracing the incorporation of 14C. While a preliminary experiment showed an enhanced incorporation of activity into cellulose and a decreased incorporation of activity into pectins, later results, from frequent observations during the onset of deficiency and the study of the metabolism of segments from different regions of normal roots, showed that differences between deficient and normal root apices were largely due to the greater age of the constituent cells of the former. Differentiation continued during boron deficiency and the changes of incorporation into pectic substances, holocellulose, lignins, sugars, and amino-acids paralleled those found during differentiation of normal roots. Two results, namely an increased incorporation of activity into pectic substances and an increased acid resistance occurred sufficiently early to be possible primary effects of deficiency although they are difficult to relate to each other. The results, with other published evidence, suggest that boron is concerned with cell-wall bonding.