Page 7 - Lesson Notes-Morphologyof flowering plant

Mentha piperita (peppermint).
* Offsets These weak stems are one internode long, stout, slender and runs
horizontally and terminates in a bud at a short distance that develops into
adventitious roots, e.g., Pistia (water lettuce), Eichhomia (water hyacinth), etc.
iv. Underground Stems
The stem of some plants lie below the soil surface. They are non-green, store food
as means of perennation and vegetative propagation.
They are of following types
(a) Rhizome It is a prostrate thick stem growing horizontally beneath the soil surface.
It has distinct nodes and internodes. The. nodes bear small scale leaves with buds in
their axils, e.g., Zingiber (ginger officinale), Curcuma domestica (turmeric).
(b) Suckers These are non-green slender stem that grows horizontally in the soil and
ultimately comes out to form a new aerial shoot. Each sucker contains one or more
nodes with scale leaves and axillary buds, e.g., Mentha (podina), Chrysanthemum
(guldaudi).
(c) Corm It is a swollen condensed form of rhizome which grows in the vertical
direction in the soil. It stores a large amount of food, e.g., Amorphophallus,
Colocasia (taro).
(d) Tuber It is a swollen end of underground stem branches. Each tuber has many
notches on the surface called eyes or buds, which grow into new plants, e.g,
Solanum tuberosum (potato).
(e) Bulb It is a highly reduced disc like stem. It bears a large number of fibrous
adventitious roots at its base. Leaf bases form bulblets. The bulblets grow into new
plants, e.g., Allium cepa (onion), Allium sativum (garlic).
Branching Pattern of Stem
The stems may be branched or unbranched.
Branching in stems may be dichotomous and lateral.
(i) The dichotomous branching occurs by the division of the apical growing point or
bud into two equal parts in a forked manner. It occurs in lower plants-cryptogams
(non-flowering plants), higher plants~Hyphaene (palm), Canscora, screw pine, etc.
(ii) The lateral branching occurs from the axillary buds of the nodes, e.g., Pinus,
grapevine, etc.
Functions of Stem
Stems perform various primary and secondary functions.
Primary Functions
(a) It bears leaves, fruits, flowers and seeds in position.
(b) It conducts water and minerals to roots, leaves, flowers, fruits, etc.
(c) It holds flower in suitable position, so that pollination and fertilistaion takes place.
Secondary Functions
(a) Many stems store food as reserve food materials.
(b) Some stems also help in photosynthesis and vegetative propagation.
(c) The underground stems help in perennation.
(d) Stem branches provide support to its various parts.
Modification of Stem
The various forms of aerial stem modification are following
i. Stem Tendrils
These are thin, long and sensitive structures which can coil around a support.
Tendrils can be of following types on the basis of their origin (d) Axillary Arise from