Sentence:  Root and stem tumors from sweet clover plants infected with WTV were quick-frozen in liquid nitrogen , embedded in ice , and cut at 3 - 6 | <WSD>m</WSD> in a cryostat maintained at - 16 ` to - 20 ` . 
Meaning of the word marked with <WSD> tags:  the basic unit of length adopted under the Systeme International d'Unites (approximately 1.094 yards)