Page 15 - LN-ANATOMY OF FLOWERING PLANT

3 Endodermis
It is single-layered and made up of barrel-shaped cells which do not enclose
intercellular spaces. The young endodermal cells possess an internal strip of suberin
and lignin, which is known as casparian strip. Endodermal cells lying opposite the
protoxylem groups however, remain in the primary stage with usual casparian strip.
These unthickened cells are called passage or transfusion cells. These cells helps in
conduction of fluids and minerals from cortex into the xylem.
4. Stele
All tissues inside the endodermis, i.e., pericycle, vascular bundles and pith form the
stele.
i. Pericycle It forms the outer boundary of stele. Pericycle may be uniseriate (single
layered) or multiseriate (multilayered).
The pericycle does not form cambium. It only produces lateral roots. The pericycle is
composed of thin-walled parenchymatous cells in a young root. Later, it becomes
thick-walled in many monocot roots.
ii. Vascular strand Vascular strand is in the form of several alternate and radial
xylem and phloem bundles. The vascular bundles are arranged in the form of a ring
around a central pith.
The xylem bundles are exarch, i.e., protoxylem lies towards the outside while, the
metaxylem faces inwards. Due to the pressure of numerous xylem bundles and
exarch condition, the xylem of monocot root is polyarch.
Protoxylem vessels are narrow while, the metaxylem vessels are the broad. Xylem
provides mechanical strength and helps in conduction of water and mineral salts.
Phloem and xylem are separated from each other by means of a narrow strip of
conjuctive tissue. The phloem cells stored food, if parenchymatous. They provide
mechanical strength on becoming sclerified. They are involved in the formation of
cambium.
iii. Pith It is large and well-developed. It is large and made up of parenchymatous
cells with intercellular spaces. These cells contain starch.
Features for Identification of Monocotyledonous Root
Monocotyledonous root can be easily identified with the following features
(i) Presence of root hairs.
(ii) Endodermis with passage cells.
(iii) Presence of pith.