In the root cortex,Fusariumusually grows in the walls and intercellular spaces, but in the stele it grows within the cells. It does not appear in the large central tracheal tubes. Hyphal strands have a tendency to grow longitudinally in and on the root. Mechanical force is involved in splitting the walls as the fungus grows within the walls. Chemical action is involved in wall penetration. Papillae form opposite penetrating pegs but disappear soon after theFusariumhyphae have penetrated the wall or passed through the papillae.