Fig. 6.8-4b. Magnification of a root apex of corn. The boundary between the root proper and root cap is distinct. An important aspect of zonation is not visible in any histological preparation like this -- much of the root apical meristem that is visible here is mitotically quiescent -- the quiescent center can only be revealed by supplying the root with radioactive thymidine and checking to see if the nuclei are synthesizing DNA (if they are, the nuclei will become radioactive; if the nuclei are not preparing for mitosis, the nuclei will not become radioactive).