Sentence:  Arrows were anciently made of reeds, afterwards of cornel wood, and occasionally of every species of wood: but according to Roger Ascham, ash was best; arrows were reckoned by <WSD>sheaves</WSD>, a <WSD>sheaf</WSD> consisted of twenty-four arrows. 
Meaning of the word marked with <WSD> tags:  A quantity of arrows, usually twenty-four.