POISONOUS PLANTS. Among the wild plants of British fields and hedgerows and included in cultivated species are a con siderable number which are more or less poisonous—some of them severely so. Many cases of poisoning have been recorded and several English works on poisonous plants have been published in the last hundred years. There is a considerable European literature on the subject, and it is largely to this that we are indebted for existing knowledge of the toxic effects of plants on farm stock.
It is not necessarily every part of a given plant which is poi sonous : the toxic property may be solely in the root or foliage or seed, while in other species all parts of the plant may be poisonous. Further, some species may be injurious in the green state but comparatively harmless when dried, the toxic principle being vola tile. Some poisonous species are commonly avoided by stock as well as by mankind, often perhaps because they are in one way or another unattractive. Some animals, however, may develop a sort of depraved appetite for a certain species, the poisonous principle of which, while not immediately and visibly toxic in its effects, may, when continuously taken, prove cumulative and eventually induce poisonous symptoms ; this is believed to be the cause of the poisoning of horses by horsetails (Equisetum spp.) and bracken. Another point of interest is that all animals are not affected alike by the same species of poisonous plant : some may be much mere easily affected than others. For example, Cornevin observes that, per too lb. live weight, it may take twice as much fresh root of water dropwort (Oenanthe crocata L.) to cause poisoning in sheep as in horses.
A further complication arises from the fact that a given species may not be equally poisonous in all districts and in different sea sons, owing perhaps to variations in climatic and soil conditions; and in this connection it is worthy of note that variations in the percentage content of the toxic principle have been observed in cases where certain species, e.g., henbane and deadly nightshade, have been grown for medicinal purposes.
Apart from a fair number of wild plants which are well known to be poisonous there must be included a considerable number of species which are under suspicion; there are yet others which affect the meat or milk of animals which feed upon them ; and it may usefully be mentioned here that there are yet others which, though not poisonous, on account of their hard or spinous character may have injurious effects on the mouths of animals when taken mixed with other herbage.
In general it may be expected that poisoning of live stock by wild plants is mainly likely to occur when they are at pasture, and the injurious species may usually be sought in the pasture itself or the surrounding hedgerows. Injurious species, however,
may also occur in arable land and may find their way to stock in the form of fodder, or, as in the case of corn cockle, included in cereal grains.
The legal aspect presented by the occurrence of some poisonous plants deserves to be borne in mind—in particular the possibility of a poisonous species overhanging a neighbour's boundary to the detriment of the neighbour's stock. It has, for example, been held in Great Britain that where a yew tree grew through and over a fence and projected on to a meadow occupied by the plaintiff, the owner of the tree was liable for the loss of a horse which was poisoned by eating the foliage of the tree.
It should also be added that poisoning of live stock sometimes occurs through the inclusion of injurious feeding stuffs in their ration, such as Java beans, the so-called Indian peas, castor-oil beans and occasionally greened potatoes. The writer has defined a really poisonous plant as "one, a small quantity of which, when eaten, induces some form of indisposition, with irritant, narcotic or nervous symptoms, with serious or even fatal consequences, either immediately, or by reason of cumulative action of the toxic property." Poisonous the British species which may be regarded as distinctly poisonous and as having in many cases proved fatal to live stock may be mentioned the following:— Lesser spearwort (Ranunculus fiammula L.) ; celery-leaved butter cup (Ranunculus scleratus L.) ; acrid buttercup (Ranunculus aver L.) ; stinking hellebore (Hellebores foetidus L.) ; green hellebore (Helle bores viridis L.) ; monkshood or aconite (Aconitum Napellus L.) ; marsh marigold (Caltha palustris L.) ; laburnum (Cytisus laburnum L.) ; cherry laurel (Prunus Laurocerasus L.) ; white bryony (Bryonia dioica L.) ; hemlock (Conium maculatum L.) ; cowbane or water hem lock (Cicuta virosa L.) ; water dropwort (Oenanthe crocata L.) ; rag wort (Senecio Jacobaea L.) ; deadly nightshade or dwale (Atropa belladonna L.) ; henbane (Hyoscyamus niger L.) ; bitter-sweet or woody nightshade (Solanum Dulcamara L.) ; thorn apple (Datura stramonium L.) ; foxglove (Digitalis purpurea L.) ; dog's mercury (Mercurialis perennis L.) ; annual mercury (Mercurialis annua L.) ; acorns (Quercus spp.) ; yew (Taxus baccata L.) ; meadow saffron (Col chicum autumnale L.) ; lords and ladies, or cuckoo pint (Arum maculatum L.) ; ergot (Claviceps purpurea Tul.).