Page 18 – Apical growing region of stem
Fig. 15 . Apical growing region of stem. A. Radial section of the apex of the stem from a 4-months-old plant to show the earliest stage of leaf initiation. a, outline of a radial section of the apical region to show the apical dome (i.e., most distal portion of the growing region), ad; leaf primordia and young leaf, l₁, l₂ and l₃, (listed in order of initiation); and first evidence of the initiation of the youngest leaf primordium, l₄, between x and x₁. Apical limit of the latter priordium is indicated at al. X40. b, meristematic tissue in the portion of the stem apex (demarcated by x-x₁, in a) in which the youngest leaf primordium (l₃, in a) is being initiated. al, apical limit; d, dermal layer (i.e., row) of cells; d1, dermal cells with anticlinal divisions; l₂o, outline of an older, over-arching leaf primordium (l₂, in a), adaxial surface; n, nucleus; sd, subdermal cells; sd₁, subdermal cells with periclinical divisions; sd₂, with oblique divisions. X400. B. Transverse section of the apical meristem of the stem (cut just beneath the surface of the apex) to show the apical cells (large cells) and dermal cells (small cells) on the side of the apical dome. X400. C. Same, cut 15/ᵘ below the section seen in B, to show the cells of the meristem. n, nuclei. X400.