Root and Shoot Studies
The Stem
The portion of plant above the ground is
known as the stem, which consists of the shoot system of the plant (leaves,
stem, flower and fruit). It develops from the plumule part of the embryo. The
regions of the stem where leaves are born are called nodes while inter-nodes are the
portions between two nodes.
Figure: Morphology of stem
Functions of stem:
·
It supports and holds leaves, flowers, and
fruits.
·
The stem allows the leaves to arrange in a
way that they are able to receive direct sunlight in order to efficiently
perform photosynthesis. The arrangement and position of leaves also allow gaseous
exchange.
·
The xylem and phloem present
in the vascular bundles of stems conduct water and minerals across the plant.
·
Stems bear flowers and fruits in a
position that facilitates the processes of pollination, fertilization, and
dispersion of seeds.
·
Some stems undergo modification to store
food and water. Example: succulents.
·
Few green stems contain chloroplasts and
are capable of carrying out photosynthesis as well.
·
Some stems are modified to carry out
vegetative propagation which is a form of asexual reproduction seen in plants.
Modifications of stem:
·
Underground stems of potato,
ginger, turmeric, colocasia are modified to store food in them.
·
Stem tendrils which develop from axillary buds, are slender and
spirally coiled. They help the plants to climb such as in gourds (cucumber,
pumpkins, watermelon) and grape vines.
·
Axillary buds of stems may also get modified into woody, straight and
pointed thorns. Thorns are
found in many plants such as Citrus, Bougainvillea. They protect plants from
browsing animals.
·
Some plants of arid regions modify their stems into flattened (Opuntia),
or fleshy cylindrical (Euphorbia) structures. They contain chlorophyll and
carry out photosynthesis.
·
Underground stems of some plants such as grass and strawberry, etc.,
spread to new niches and when older parts die new plants are formed.
Figure: General anatomical
outline of dicot and monocot stem
Anatomy of stem:
Stem consists of multi-cellular
epidermal hairs, epidermis, parenchyma (sclerenchymatous), vascular bundle, pith
and ground tissue or ground meristem from outer to inner.