The discussion in this paper is based on a study of the changes induced by boron deficiency in garden beet (Beta vulgaris) and cabbage (Brassica oleracea var. capitata). The first pathologic effects are physiological and tend to speed up cell division and cell growth. Wall-formation and cell-differentiation are concurrently interrupted. Necrosis follows, and the by-products released from dead or dying cells may also become factors influencing growth of surrounding cells. In vascular cambium the result is a deficiency in conducting elements and consequent secondary effects on plant growth. In storage tissue, as in cabbage pith, necrosis is accompanied by hypertrophy and hyperplasia as well as by abnormal differentiation into various types of thick-walled cells. Symptoms may be only microscopic and, therefore, borax applications to the growing crop may result in an increase in yield over that of untreated controls even though macroscopic signs of B deficiency do not appear in the latter.