pith in the centre and pericycle, endodermis, cortex
and hypodermis respectively towards the outer side.
• The shoot apical meristem forms three histogens:
dermatogen, periblem and plerome (Hanstein’s histogen
theory, 1870). Dermatogen forms epidermis, periblem
forms cortex and plerome forms stele (the part inner to
endodermis). Central part of plerome which forms vascular
tissues is called procambium.