=Legal Aspect of Plant Poisoning.= There is clearly some legal liability in regard to poisonous plants which may, by hanging over a boundary, cause injury to a neighbour’s stock. The only cases known to the author are in relation to the yew. In the case of _Crowhurst v. Amersham Burial Board_ (48 L. J., Ex. 109; 4 Ex. D., 5) a Burial Board was held liable for the loss of a horse poisoned by eating leaves of a yew tree planted in the cemetery owned by the Board, the tree having grown through and over their fence and projected on to the meadow occupied by the plaintiff. In _Ponting_ v. _Noakes_ (63 L. J. B. 549; (1894) 2 Q.B., 281) the defendant was not held liable for the death of a horse which ate off the branches of a yew tree, because the tree did not extend up to or over the plaintiff’s boundary, though it overhung a ditch, the edge of which was the boundary, and was hence accessible to the plaintiff’s stock. =The Toxic Principles of Plants.= The poisonous substances in plants may be grouped either (1) according to their physiological effects on certain organs; (2) according to the principal outward and perceptible symptoms caused; or (3) in accordance with their chemical relationships. In regard to (1) the poisons may be nerve, heart, blood-poisons, etc. (2) The poisons may be acrid, narcotic, or both. _Acrid poisons_ are those which cause irritation or inflammation of the digestive tract (_Euphorbia_, _Ranunculus_, _Daphne_, _etc._); _narcotic poisons_ affect only or chiefly the brain (_Agrostemma_, _Papaver_, _Atropa_) or chiefly the spinal cord (_Claviceps purpurea_, _Lolium temulentum_); _acrid-narcotic poisons_ induce to a greater or less extent the symptoms of both the foregoing groups (_Taxus_, _Colchicum_, _Cicuta_, _Solanum_, _etc._). (3) As the accounts of the individual plants will show, the toxic principles of many plants are not yet well understood, either as regards chemical constitution or symptoms caused. Many poisons may be driven off by heat (boiling, drying), and some plants may thus be rendered harmless. Most of the toxic principles of our native poisonous plants are Alkaloids or Glucosides. The former all contain nitrogen, differ considerably in molecular constitution, and are usually combined with widely distributed organic acids. In the pure state they are colourless and usually stable, crystalline or amorphous solids, or readily volatile liquids; they usually have a burning taste. In general the same base is confined to species of the same order—_e.g._ Solanine to the _Solanaceæ_. The alkaloids include the most powerful poisons.