Well let's take Sedimentary rock for example, The Law of Superposition which measures the average age of Sedimentary rocks using rocks around it. So you would use that rocks below it are older and that Extrusions and Intrusions are younger than the rocks which are stable.
Answer:
They have helical thickening of lignin in their walls to prevent collapse
Explanation:
the primary function of Xylem and its conducting vessels tracheids is to provide support and tranport water and minerals in plants.
Xylem vessels have layers of dead materials in the walls called LIGNIN. Lignin is a polymer; a very strong, hard materials that stop water passage through it,because it contains dead cells,
Therefore the presence of deposit of these strong impermeable, ligified walls in its walls prevent its collapse during mass flow of water of transpiration pull.
It gets passed onto the baby