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ANATOMICAL INVESTIGATION OF THE VEGETATIVE SYSTEM OF THE APRICOT (PRUNUS ARMENIACAL.)
At first the pleroma is developed.
Later on the periblem evolves from around the pleroma and covers it.
Finally the columella is developed by cell-division, mostly from the central cells.
Calyptra -originating from the columella- widen out and from it begins the dermatogen, so we can consider this as dermocalyptrogen.
In this way the classical primary structure of the root apex is developed.
The primary root is covered by hair-forming rhizodermis.
The multiseriate (5–10) primary cortical layers consist of a thin wall, roundish parenchyma cells.
Their diameter in cross-section is smaller in the outer cortex (15–20 /um) and in the inner cortex (20-30 um) than in the middle of the cortex (30–45 /um) as seen in Fig.1.
The endodermis is surrounded by an interesting, so-called "fi" (named after the Greek letter, Phi) cell layer or sheat.
This wall thickening resembles the casparian strip in cross-section, but it is considerably more.
This usually is on the corner of the cells or rather at the conjunction of 3 or 4 cells (Figure 2).
The endodermis has a casparian strip which later becomes the secondary walls.
The pericambium is commonly one layer of cells.
The vascular bundles of the stele are in radial arrangement in cross-section.
The number of xylem bundles first are two (diarch) later becoming three (triarch). The main roots -the roots of seedlings -are pentarch.
Strands of the phloem alternate with the xylem ridges.
A pith consisting of parenchyma is present (Figure 2).
In the early state of secondary growth a solid xylem cylinder and a phloem ring is developed, when the vascular cambium has already closed into a ring in cross-section.