Sentence:  Frequently a few isolated thick walled cells or , rarely , groups of such cells in the xylem region , were also specifically stained , but there <WSD>was</WSD> no such staining in epidermis , cortex , most xylem cells , ray cells , or pith . 
Meaning of the word marked with <WSD> tags:  happen, occur, take place; this was during the visit to my parents' house"