Stems

Reviews the functions of a stem, its external structures, and its internal make-up. States that plants are often recognized and referred to by their stem structures, as trees, bushes, herbs, vines, and rhizomes. Lists the three stem functions as basically strength, transportation, and storage. Pictures external structures of the stem and continues with stem tissues and pattern of arrangement as seen under a microscope. Points out the conduction cells, tracheids, and vessels; and demonstrates movement of water through them. Cites factors affecting transportation in stems as cohesiveness of water molecules, transpiration in leaf, and root pressure. Studies the structure and function of the phloem cells (in vertical transport) and ray cells (in lateral transport). Shows conduction of radioactive phosphorus P23 and resulting autoradiograph which shows pathways and accumulations of these materials in the plant.