Textbook of pharmacognosy and phytochemistry 1st Edition unsecured

44 TEXTBOOK OF PHARMACOGNOSY AND PHYTOCHEMISTRY
root. It grows further to produce branches in the
acropetal manner known as secondary roots which
further branches to give tertiary roots. These are
all true roots. This system is characteristic of
dicotyledons.
(b) Adventitious root system: The roots that develop
from any part of the plant other than radicle are
termed as adventitious roots. They may develop
from root base nodes or internodes. This type of
root system is found in monocots and in pteridophytes.
(a)
Fig. 4.19 (a) Tap root system and (b) Adventitious root system
I. Modification for storage of food: This type of modification
is shown by both the types of roots, i.e. tap roots and
adventitious roots. They store carbohydrates and are used
during early growth of successive season.
(i) Tap roots show the following three types of modifications:
(a) Conical: These are cone-like, broader at the base
and tape-ring at the tip, e.g. carrot.
(b) Fusiform: These roots are more or less spindle
shaped, i.e. tapering at both the ends, e.g. radish.
(c) Napiform: These are spherical shaped and very
sharply tapering at lower part, e.g. beat and turnip.
(b)
(a) Tuberous roots: These get swollen and form single
or isolated tuberous roots which are fusiform in
shape, e.g. sweet potato, jalap, aconite.
(b) Fasciculated tuberous roots: When several tuberous
roots occur in a group or cluster at the base
of a stem they are termed as fasciculated tuberous
roots as in dahlia, asparagus.
(c) Palmated tuberous roots: When they are
exhibited like palm with fingers as in
common ground orchid.
(d) Annulated roots: The swollen portion is in the
form of a series of rings called annules as in
ipecacuanha.
II. Modifications for support: Plant develops special
aerial roots to offer additional support to the plant by way
of adventitious roots.
(a) Clinging or Climbing roots: These types of roots
are developed by plants like black pepper for
support or for climbing purposes at nodes.
(b) Stilt roots: This type of root is observed in maize
and screw-pine, which grow vertically or obliquely
downwards and penetrate into soil and give additional
support to the main plant.
(c) Columnar roots: In certain plants like banyan, the
additional support is given by specially developed
pillars or columnar roots. They even perform the
function of regular roots.
(a) (b) (c)
Fig. 4.21 (a) Climbing root (b) Stilt root (c) Columnar root
(a)
(b)
Fig. 4.20 (a) Conical root, (b) Fusiform root and (c) Napiform
root
(ii)
Adventitious root show the following types of modifications.
They store carbohydrates but do not assume
any special shape.
(c)
III. Modifications for special functions:
(a) Respiratory roots or pneumatophores: The roots
of the plant growing in marshy places on seashores
due to continuous water logging are unable
to respire properly. They develop some roots
growing against the gravitational force (in the
air) with minute openings called lenticels. With
the help of lenticels they carry on the exchange
of gases. They look like conical spikes around
the stems. This type of root is observed in case
of plants called mangroves found in creeks, i.e.
avicinnia.
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