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.
This plant has been in cultivation from very ancient times. Its stems produce the fibre of linen, and its seeds are used for oil and feed. In western Canada where the plant is raised extensively for its seed, disastrous effects have come from the feeding of screenings containing immature flax bolls and frozen flowers.
J. R. Dymond, late of the Seed Branch, Ottawa, received a sample of flaxseed screenings with the following statement from a farmer in Saskatchewan: "A few weeks ago I fed about three gallons to a cow and two gallons to a heifer. Both were in convulsions in less than twenty minutes. The heifer died in about two hours, the cow in about eight hours." On analysis the sample was found to consist of: immature flax bolls and chaff, 75%; flaxseed, 18%; wheat, 4%; weed seeds, 2%. A chemical analysis showed a considerable proportion of prussic acid. Corroborative reports have come from other places where screenings containing immature flax bolls have been fed, and it is now an established fact that they develop prussic acid in sufficient quantity to make them dangerous in feeds.
The plant is too widely cultivated to need description here.