Sentence:  Frequently a few isolated thick walled cells or , rarely , groups of such cells in the xylem region , were also specifically stained , but there was no such staining in epidermis , cortex , <WSD>most</WSD> xylem cells , ray cells , or pith . 
Meaning of the word marked with <WSD> tags:  (superlative of `many' used with count nouns and often preceded by `the') quantifier meaning the greatest in number