Matthew Velkey, Ph.D., Lecturer, Department of Cell and Developmental Biology, University of Michigan Medical School

This image shows a stem of a corn plant (Zea mays), cut in cross-section and stained with dyes that react with different sugars found within the various structures.  Much of the stem consists of air spaces and parenchymal (support) cells.  Scattered in the parenchyma are vascular bundles made of cells lined end to end that transport water and nutrients up and down the stem of the plant.  Each bundle is ensheathed by a tough layer of fiber cells (small green circles around each of the “faces”).  Within the bundles are xylem vessels (the green “eyes”, “nose”, and “mouth” of each face).  Also present are various phloem vessels (the red circles in the “forehead”) that transport sugars and other substances made by the plant. The observation that the xylem and phloem are so regularly arranged suggest a patterning mechanism that is as yet not fully understood.