Fig. 6.3-4. Magnification of coleus (Coleus) shoot apical meristem. Coleus, like almost all flowering plants, have a tunica-corpus organization. Cells in the outermost layer divide only anticlinally (new walls are perpendicular to the apex surface), not periclinally. Look at the outermost layer carefully, following it from the left side to the right. All cells are close to the same height, none is so short as to suggest it has resulted from a periclinal division. Notice that even the second layer of cells is so uniform that it can be traced from left to right as being just a single layer -- the tunica on this apex is two layers thick (the two layers between the sets of arrows). Now examine the third layer; it is uniform in most places, but is not really distinct in the center -- I would call this a part of the corpus, others might consider it a third tunica layer. The fourth layer is definitely too irregular to be tunica. The cells in the lower center of the micrograph are so vacuolate they have more of a white color than red -- these are pith-rib meristem cells. The smaller, redder, more orderly cells along the two side of the apex are peripheral zone cells.