During the last ten or fifteen years much progress has been made in interpreting the role of imbibition, or colloidal hydration and swelling, in plant life. Formerly associated mainly with the energetic swelling of organic matter, and with certain movements of deformation, such as warping curvatures, twisting of awns and carpellary valves, bursting of capsules, and throwing of seeds and spores, it is now recognized as one of the major influences in organic process. It is important in initiating the germination of seeds, plays a prominent role in the early phases of growth of cells and tissues, apparently bears a relation to the origin of succulence and xeromorphy, is a vitally important factor in the protection of hardy plants from winter injury by freezing, in the hardening of plants to cold, and is probably equally important along with osmotic pressure, as a factor in the absorption, transfer, and distribution of water throughout the body of the plant. A few facts may be presented in regard to each of these functions before proceeding to a detailed discussion of the problems of development of saturation deficit in leaf colloids, the energetics of transfer, and the absorptive functions of