This section is from the book "A Guide To The Poisonous Plants And Weed Seeds Of Canada And The Northern United States", by Robert Boyd Thomson, H. B. Sifton. Also available from Amazon: A guide to the poisonous plants and weed seeds of Canada and the northern United States.
Brassica arvensis (L.) Ktze., Brassica Sinapistrum Boiss.
Other Common Names: Charlock, Herrick.
The poisonous properties of this plant have been given less attention in America than they deserve. The reason is a natural one. The seeds only are harmful, and the plant is uncommon in hay and probably would be rejected if present. It thus happens that animals obtain the poison only when the seeds are combined with concentrated feeding stuffs. This very often happens, but the nature of the seed is such that when finely ground, an ordinary inspection fails to distinguish it from the wheat middlings with which it is often mixed, and so its harmful effects have been attributed to other causes.
A typical case of its action may be cited. A sample of shorts was received from a farmer, together with complaints that two of his pigs were already dead, and that the same would have been true of all the rest had he not discontinued the use of the feed. On casual examination, the sample appeared excellent. The microscope, however, revealed the pre-sense of quantities of Mustard seed, very finely ground. The seed, which must have been deliberately added to the shorts, had served two purposes. In the first place it was a cheap adulterant, and secondly, it raised the fat and protein content of the feed as shown by chemical analysis.
A Case of Poisoning
Fig. 22. - Seeds of Wild Mustard - Brassica arvensis. Five times natural size.
A request for further information brought the following reply from the farmer: "The pigs came up to the trough and after feeding would fall back in a fit and kick about two minutes, then jump up and stagger a little. After wandering around the pen for a few days they died, eating little in the meantime. They showed agony when dying, kicking and frothing at the mouth."
*The complete separation of weed seeds is an essential preliminary to the milling of wheat, as otherwise a good grade of flour is not produced. Bran and shorts are therefore pure when they come from the mill.
Doubtless a trained observer would have detected other symptoms, but a comparison of those just stated with the typical symptoms of Wild Mustard poisoning will leave no doubt as to the cause of the trouble. According to Mueller, as quoted by Long, these are: "Inflammation of the stomach and intestines (with loss of appetite, wind, colic and diarrhoea); inflammation of kidneys (difficult, excessive or bloody urination); and nervous symptoms, with great exhaustion, uncertain gait, paralysis of limbs, and, in isolated cases, convulsions." Horses and cattle are affected to some extent, but pigs suffer most injury.
The poisonous constituents are three in number: volatile oil of mustard, the alkaloid sinapin, and the alkaloidal glucoside sinalbin. The plant was introduced from Europe and has spread across the continent, in grain fields and waste places. Although an annual it is a very bad weed on account of its numerous seeds. When buried in the soil they can live for many years. The plant is simple or branching, one to three feet high, with its upper leaves stemless, and the lower ones petioled and usually lobed. The stem is purple at its junction with the branches. The fragrant, bright yellow flowers, two-thirds of an inch in diameter, are in clusters at the tips of elongating racemes. The seed pods are slender and one to two inches long. They are knotted below and terminate in a two-edged beak.
The round, black seeds are about one-sixteenth of an inch in diameter, and slightly roughened. They resemble the seeds of some other Brassicas very closely, but can be distinguished from them by the microscopic and chemical characteristics of their coats. The epidermis or colourless outer layer of the seed coat has each cell almost filled with vertical columns of mucilage grouped about a central cavity. Beneath, is the sub-epidermal layer and then the palisade cells, filled with a dark substance which turns red when warmed with concentrated solutions of hydrochloric acid and chloral hydrate in the proportion of one to twenty. Inside the palisade is an opaque, pigmented layer, while the centre of the seed contains oil and aleurone grains. It is here that the poison is located.