What are the classification of meristematic tissue?
Classification of meristems
- On the basis of origin and development
- On the basis of position in plant body
- On the basis of plane of cell division
i) On the basis of origin and development, meristems are of 3 types.
b) Primary meristem
c) Secondary meristem
- It is situated at the tip of root and the stem.
- It is the first formed meristematic region and can be regarded as embryonic stage for other developing meristems.
- The derivatives of promeristem can give rise to all types of primary tissues.
- This meristem is also said to be primordial meristem, embryonic meristem or urmeristem.
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- It is a derivative of promeristem which continues to divide and later the derivatives differentiate into permanent tissues.
- They are formed from permanent tissue after dedifferentiation.
e.g. Interfascicular cambium, Vascular cambium of root, phellogen, wood cambium, accessory cambia.
ii) On the basis of position in plant body meristems are of three type
a) Apical meristem
b) Intercalary meristem
c) Lateral meristem
- They are present at the tip of root and stem.
- They take part in initial growth or elongation of roots and stems.
- This is located away from apical meristem, between the two differentiated regions. e.g. at the base of internodes in grass, at the base of leaves in Pinus, or at the base of nodes in Menthea.
- They are present along the side of central longitudinal axis.
- They increase the girth of the plant by producing secondary vascular tissue.
- The thin walled cells of vascular cambium are highly vacuolated unlike other meristematic cells. e.g. Cork cambium or Phellogen.
iii) On the basis of plane of cell division meristems are of three types -
a) Mass meristem
b) Plate meristem
c) Rib or file meristem
They divide in almost all the planes e.g. endosperm.
They divide in two plane at right angle to each other and form plate like structure.
e.g. epiblema, epidermis etc.
- They help in formation of uniseriate epidermis and multiseriate blade of the leaf.
- The cells of this meristem divide at right angle to the longitudinal axis (i.e., anticlinally) to form longitudinal files of cells.
e.g. The cortex and the pith in roots and stems are formed by rib meristem.
iv) On the basis of function, meristems are of three types
c) Ground meristem
They form epidermis
They produce primary vascular tissue.
The cells of this region are large, thin walled and isodiametric. These produce hypodermis, cortex, endodermis, pericycle, medullary rays and pith.