I learnt that lignin impregnates xylem cells, causing the cytoplasm to die due to the inability of water and nutrients to pass freely, hence creating hollow tubes adapted to transport materials. This means that in order for the cytoplasm to die and the tubes to be hollow, lignin needs always be present.. However lignin is not present in all xylem vessels... Lignin is the woody tissue that only forms the trunk of a tree. So how do these cells hollow out in other parts of the plant/tree to create empty transport vessels..??