Anatomy of Flowering Plants 2 Flashcards
explain outermost layer of dicot stem
The transverse section of a typical young
dicotyledonous stem shows that the epidermis
is the outermost protective layer of the stem.Covered with a thin layer of cuticle, it may bear trichomes and
a few stomata. The cells arranged in multiple layers between epidermis and
pericycle constitute the cortex. It consists of three sub-zones.
what are the zones of the cortex
The outer
hypodermis, consists of a few layers of collenchymatous cells just below the
epidermis, which provide mechanical strength to the young stem. Cortical
layers below hypodermis consist of rounded thin walled parenchymatous
cells with conspicuous intercellular spaces. The innermost layer of the cortex
is called the endodermis. The cells of the endodermis are rich in starch
grains and the layer is also referred to as the starch sheath.
explain vascular bundle region in dicot stem
Pericycle is present on the inner side of the endodermis and above the phloem in the
form of semi-lunar patches of sclerenchyma. In between the vascular bundles
there are a few layers of radially placed parenchymatous cells, which constitute
medullary rays. A large number of vascular bundles are arranged in a ring ;
the ‘ring’ arrangement of vascular bundles is a characteristic of dicot stem.
Each vascular bundle is conjoint, open, and with endarch protoxylem. A
large number of rounded, parenchymatous cells with large intercellular
spaces which occupy the central portion of the stem constitute the pith.
describe monocot stem
The monocot stem has a sclerenchymatous hypodermis, a large number
of scattered vascular bundles, each surrounded by a sclerenchymatous
bundle sheath, and a large, conspicuous
parenchymatous ground tissue (Figure
6.4 b). Vascular bundles are conjoint and
closed. Peripheral vascular bundles are
generally smaller than the centrally
located ones. The phloem parenchyma is
absent, and water-containing cavities are
present within the vascular bundles. The protoxylem dissolves to form protoxylem lacuna. endarch arrangement of xylem/
explain the epidermis of dicot (dorsiventral) leaf
The vertical section of a dorsiventral leaf
through the lamina shows three main
parts, namely, epidermis, mesophyll and
vascular system. The epidermis which
covers both the upper surface (adaxial
epidermis) and lower surface (abaxial
epidermis) of the leaf has a conspicuous
cuticle. The abaxial epidermis generally
bears more stomata than the adaxial
epidermis.The latter may even lack
stomata
explain mesophyll of dorisventral leaf
The tissue between the upper
and the lower epidermis is called the
mesophyll. Mesophyll, which possesses
chloroplasts and carry out
photosynthesis, is made up of
parenchyma. It has two types of cells – the
palisade parenchyma and the spongy
parenchyma. The adaxially placed
palisade parenchyma is made up of
elongated cells, which are arranged
vertically and parallel to each other. The oval or round and loosely arranged
spongy parenchyma is situated below the palisade cells and extends to
the lower epidermis. There are numerous large spaces and air cavities
between these cells.
explain vascular system
Vascular system includes vascular bundles, which
can be seen in the veins and the midrib. The size of the vascular bundles
are dependent on the size of the veins. The veins vary in thickness in the
reticulate venation of the dicot leaves. The vascular bundles are
surrounded by a layer of thick walled bundle sheath cells. it has xtlem towards adaxial end and phloem towards abaxial end. no cambium present
explain monocot leaf
The anatomy of isobilateral leaf is similar to that of the dorsiventral leaf in
many ways. It shows the following characteristic differences. In an
isobilateral leaf, the stomata are present on both the surfaces of the
epidermis; and the mesophyll is not differentiated into palisade and spongy
parenchyma. The parallel venation in monocot leaves is reflected in the near similar
sizes of vascular bundles (except in main veins) as seen in vertical sections
of the leaves.
what are bulliform
In grasses, certain adaxial epidermal cells along the veins modify
themselves into large, empty, colourless cells. These are called bulliform
cells. When the bulliform cells in the leaves have absorbed water and are
turgid, the leaf surface is exposed. When they are flaccid due to water
stress, they make the leaves curl inwards to minimise water loss.
