It is hard to delimit regions of the SAM based on cell size and staining. The outer Tunica layer is obvious in virtually all SAMs. One can usually point to the general location of the Corpus because of the rapid enlargement and vacuolation. However, this is rather vague and imprecise. Gymnosperm SAM - Note the relatively large size and faint staining of cells in the apex center.
Mitotic cells synthesize DNA rapidly.
However, subtending cells in both regions are heavily labeled. Experiments with several species have yielded similar results. When the rates of cell division were carefully and painstakingly analyzed in SAMs, it became clear that the apical quiescent cells did not divide frequently. However, they did divide given sufficient time. The cells on the periphery of the QC labeled heavily with thymidine and divided rapidly.