Sentence:  Schramm and Rottger ( 1959 ) did not report any such nonspecific staining of plant tissues with <WSD>fluorescein</WSD> isocyanate labeled antiserum to tobacco mosaic virus . 
Meaning of the word marked with <WSD> tags:  a yellow dye that is visible even when highly diluted; used as an absorption indicator when silver nitrate solution is added to sodium chloride in order to precipitate silver chloride (turns pink when no chloride ions are left in solution and negative fluorescein ions are then absorbed)