These are primitive type of conducting elements found in Pteridophytes and Gymnosperms. Sieve cells have sieve areas on their lateral walls only. They are not associated with companion cells

Cell wall thickening in tracheids
(i) Annular
(ii) Spiral
(iii) Reticulate

(i) Textile fibres
(a) surface fibres - Eg: Cotton
(b) Soft fibres - Eg: Flax
(c) Hard fibres - Eg: Coconut
(ii) Brush fibre
(iii) Rough weaving fibres
(iv) Paper making fibres
(v) Filling fibres

(i) Vascular bundles are scattered (atactostele) in the parenchymatous ground tissue. Each vascular bundle is surrounded by a sheath of sclerenchymatous fibres called bundle sheath.
(ii) The vascular bundles are conjoint, collateral, endarch and closed.
(iii) Vascular bundles are skull or oval shaped

(i) The radial and the inner tangential walls of endodermal cells are thickened with suberin and lignin in roots.
(ii) This thickening was first noted by Caspary. So these thickenings are called Casparian strips.
(iii) Casparian strips are absent in the endodermal cells which are located opposite the protoxylem elements.

Based on position, meristems are classified into three types.
1. Apical meristem:
Apical meristem is present in the apices of root and shoot. It is responsible for increase in the length of the plant. This kind of growth is called as primary growth.
2. Intercalary meristem:
Intercalary meristem occurs between the mature tissues. It is responsible for elongation of internodes. Eg: Grass.
3. Lateral meristem:
Lateral meristem occurs along the longitudinal axis of stem and root. Vascular cambium and cork cambium (phellogen) are example for lateral meristem. It is responsible for secondary tissues and thickening of stem and root.