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In presenting the results of the experiments which follow in this paper the writer will, for the sake of simplicity and proper evaluation of the observations, assume that the reader is familiar with the facts of electric polarity in the Douglas fir which have been presented in previous papers (LUND 1, 2, 3). It will be recalled that when electrode contacts are made at the center of the wood and any point on the outer surface in the same cross-section of the tree, the center of the wood is always electropositive (in the external circuit) to the outer surface of the cortex. This is true for all regions of the tree stem below that of the first or second apical internode. Recent observations reported below indicate that the orientation of the radial polarity in the region of the most apical internode is reversed under conditions of absence of injury or stimulation. Since all or at least the greater part of the radial P. D. is confined to the living parts of the wood-cortex system and since the cambium exhibits a bipolar structure which corresponds to the bipolar radial growth in wood and cortex, we might expect to find that the wood-cortex system including the cambium also exhibits a double electric polarity. Up to the time of the present experiments and those to be presented in following papers on the effect of temperature, it had not been possible to demonstrate with certainty whether or not the cortex possessed an electric polarity of its own. The difficulty lay in the fact that any process of separation of the cortex from the wood axis involves more or less permanent injury, due to deformation of the cortex and therefore radical change in its electric polarity. This fact is also to be expected from the experiments reported in the preceding paper which pertain to the effect of mechanical stimulation on the electric polarity. Various incidental observations seem to indicate that the radial E.M.F. per se in the wood is not affected to a noticeable degree by merely removing the cortex. This result might perhaps also be anticipated since no marked deformation of the wood occurs in such a process. The preceding facts led the writer to devise a procedure by which the existence of the E.M.F. in the cortex could be made evident without injury or at least with a minimum of injury to the cortex. The principle of summation of electric polarities of cells, which has been fully stated in previous papers, is obviously of fundamental impor-

ELECTRIC CORRELATION BETWEEN LIVING CELLS IN CORTEX AND WOOD IN THE DOUGLAS FIR