This paper expressed the belief that the acridity of the Indian turnip and other plants belonging to the same family, was due to the presence of needle-shaped crystals or raphides found in the cells of these plants. This conclusion was not accepted by Professor T. J. Burrill, of the University of Illinois, nor by other eminent botanists who were present and took part in the discussion that followed the reading of the paper. The opposition was based mainly on the well-known fact that many other plants like the grape, rhubarb, fuchsia, spiderwort, etc., are not at all, or but slightly acrid, although the raphides are as abundant in them as in the Indian turnip and its allies. Up to this time the United States Dispensatory and other works on pharmacy, ascribed the following rather indefinite cause for the acridity of the Indian turnip. It was said to be due to an acrid, extremely volatile principle. This principle was insoluble in water and alcohol, but soluble in ether. It was dissipated both by heating and drying, and by this means the acridity is destroyed. There was no opinion given as to the real nature of this so-called principle. More recently it has been intimated that the acridity may be due to some ferment or enzyme, which has been derived in part from the self-decomposition of protoplasm and in part by the process of oxidation and reduction. Here the question appeared to rest. At all events I was unable to glean any further knowledge from the sources at my command. Some time later the subject was taken up in a more comprehensive manner and the following report is the first detailed description of an investigation that has occupied more or less of my leisure for some years. A dozen or more species of plants have been used for examination and study. Among these were: Indian turnip (Arisoema triphyllum). Green dragon (Arisoema dracontium). Sweet-flag (Acorus). Skunk cabbage (Spathyema). Calla (Richardia). Caladium (Caladium). Calocasia (Calocasia). Phyllodendron (Phyllodendron). Fuchsia (Fuchsia). Wandering Jew (Tradescantia). Rhubarb (Rheum). Grape (Vitis). Onion (Allium). Horse-radish (Armoracia). Most of the plants selected were known to have crystals in certain parts. Some of them were known to be intensely acrid. In these the acridity was in every instance proportional to the number of crystals. The following order of study was pursued and the results of each step noted. Only the more salient points of the methods employed and the conclusions reached are presented. 1. The Character of the Taste Itself.--It was readily noted that the sensation produced by chewing the various acrid plants was quite different. For example, the Indian turnip and its close allies do not give the immediate taste or effect that follows a similar testing of the onion or horse-radish. When the acridity of the former is perceived the sensation is more prickling than acrid.