Root Stem Transition in Plants (with PPT)
(Theories of Anatomical Transition from Root to Stem In Angiosperms)
Root and stem form a continuous structure in plants called the axis. The vascular tissue in root is radial (xylem and phloem arranged separately in different radii) whereas in the stem is conjoint (xylem and phloem are arranged together in same radii as vascular bundles). Thus, there should be a region in the axis where the vascular structures of the root and the stem meet and merge together. This peculiar region is called the Root-Stem Transition Zone.
The current post describes the various types of root-stem transitions found in Angiosperms.
Ø The epidermis, cortex, endodermis, pericycle and the secondary vascular tissue are continuous from root to stem.
Ø Only the primary vascular tissue in the axis undergoes a change in their position and orientation.
Ø The exarch arrangement of xylem in root changes to endarch position in the stem.
Ø In the transition zone, the vascular tissue undergoes many changes such as Forking, Multiplication, Rotation and Fusion.
Ø The vascular tissue also increases their diameter.
Ø The exact position of the transition zone is different in different plants.