The dividing line between plants which are actually poisonous and those which are only suspected is far from clear, but a division was considered desirable for the convenience of the reader, and an endeavour has been made to give a sound but brief statement as to the present information on plants poisonous to live stock in the United Kingdom, with symptoms, toxic principles, and a list of the more important references to the bibliography in relation to each plant included in Chapters II to VI (the numbers corresponding with the numbers in the Bibliography). Regarding symptoms it is to be regretted that in many cases they appear to be the result of injections of the toxic extracts, and not observations made after natural poisoning by ingestion of the plants. Further, there may frequently be doubt as to the identification of the plant suspected of causing poisoning; indeed, in some cases it is possible that the identification rests on the veterinary surgeon or the stockman _thinking_ a certain plant is the cause. The most complete and systematic account of European poisonous plants is that of Cornevin (1887), and references to poisonous plants in the ordinary literature are heavily indebted to him. In so far as the toxic principles of the plants are concerned, however, his book is in many instances no longer reliable. The chemical formulae, quoted for the use of students and research workers, have been checked by consulting works by the following authors, the reference to the bibliography being given in brackets: Henry (128), Dunstan (76), Allen (4), Haas and Hill (114), Thorpe (240), Van Rijn (252), Kobert (161), Esser (81), and Beilstein (16). Apart from the literature consulted I desire to acknowledge my great indebtedness to the Board of Agriculture and Fisheries for kind permission to make use of official records; to Mr F. W. Garnett, M.R.C.V.S., for kindly reading the proofs from the veterinary standpoint; to very many Experiment Stations, State Departments of Agriculture, and other authorities in Australasia, America and the Continent of Europe, for assistance given and literature sent; to Sir David Prain and members of the staff at Kew for much friendly advice, and aid in consulting the Kew library; to Sir James Dobbie for permission to spend some time at the Government Laboratories to consult certain volumes; to Mr T. H. Middleton, C.B., Dr. E. J. Russell, Professor W. Somerville, Sir Stewart Stockman, Professor T. B. Wood, and others, for information and many helpful suggestions; to my friend Mr W. A. Whatmough, B.Sc. (Lond.), for many suggestions and kindly reading the proofs; and to my colleague Mr W. R. Black for invaluable help in preparing notes, checking data and reading proofs. To all these, and many others who are not mentioned by name, I tender my sincere thanks. For any shortcomings I crave the indulgence of my readers, only requesting that they be friendly enough to spare a moment to call my attention thereto.