Structure of plant transport tissues

A plant, like your body, needs a plumbing system to move things around. In this lesson we open a herbaceous dicotyledonous plant and cut thin transverse sections of its stem, root and leaf, learning to identify and label every part and to use an eyepiece graticule so our drawings keep the correct proportions. We see how the vascular bundles are arranged as a ring near the edge of the stem, but as a central star of xylem in the root, and along the veins of the leaf. Then we zoom in to the cells themselves: the dead, hollow, lignified xylem vessel elements with their broken end walls and pits; the living but nucleus-free phloem sieve tube elements with their perforated sieve plates; and the busy companion cells packed with mitochondria and joined to the sieve tubes by plasmodesmata. Throughout, we relate each structure to its function, and finish with the exam skill of making a low-power plan diagram and a high-power drawing from prepared slides.