Fig. 7.1-1. Transverse section of sweet potato stem (Ipomoea batatas). This micrograph is intended as an introduction to xylem. In almost all histological slides, xylem will be stained red because of its thick, lignified walls. Many or most xylem cells will be much larger than nearby cells. These are vessel elements in transverse section; because they are mature, they have no protoplasts. They may have been filled with water being conducted when this sampled was dissected from the plant, but the water either drained out during dissection or it was removed by dehydration. You will never see slides of xylem with their water actually in them unless the material was frozen before dissection and then kept frozen until you examine it – something which is extremely difficult to do.