flax vs plow under

flax

noun
  • A plant of the genus Linum, especially Linum usitatissimum, which has a single, slender stalk, about a foot and a half high, with blue flowers. Also known as linseed, especially when referring to the seeds. 

  • The flax bush, a plant of the genus Phormium, native to New Zealand, with strap-like leaves up to 3 metres long that grow in clumps. 

  • The fibers of Linum usitatissimum, grown to make linen and related textiles. 

plow under

verb
  • To destory (crops) by turning them into the ground with a plow 

How often have the words flax and plow under occurred in a corpus of books? (source: Google Ngram Viewer )