The shoot
apex in most dicots
produces derivatives which elongate in close proximity to the apex without
much increase in stem diameter. The diameter of the stem can be increased
through the action of the Vascular Cambium.
We have already seen this!!!
Shoot apices in some monocots increase the stem's diameter close the the
apical meristem, without any internodal elongation.
This is due to the activity of a lateral
meristem known as the
"Primary Thickening Meristem"
(PTM).
|
Ti (Cordyline sp.) Shoot Tip - Note the
absence of internodal elongation & the
increase in stem diameter.
Most cells in the PTM divide periclinally
(parallel to the surface) to produce files of cells. These do not elongate very
much as they expand. This causes an increase in thickness close to the Shoot Apical
Meristem. This explains its designation as a "thickening" meristem. |