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.