Biology Today — January 2018

Branching Patterns of Stem

• The unbranched stem is called caudex or columnar, e.g., palm, sugarcane, maize.


• Branching in stem may be of two types:

Stem

branching

Dichotomous

The growing point gets divided into two in the

region of branching,e.g., Dictyota(alga),

Marchantia(bryophyta),Pandanus(angiosperm).

Lateral

The growing point does not

get divided. Racemose

The terminal bud continues its

activity indefinitely.The lateral

branches are borne over it in an

acropetal succession,e.g., Pinus,

Eucalyptus, etc.

Cymose

The terminal bud, after forming a

small portion of the axis, either

stops its activity or gets modified

into a flower, tendril, thorn, etc.

It is of three types.

Uniparous

Further growth of the stem is

continued by a single axillary branch.

The main axis is formed by the

fusion of bases of axillary branches

and the main stem. It is called

sympodial axis (sympodium)

e.g.,grapevine,.Saraca

7 6 5 4 3 2 1

Biparous

Further growth is continued by

two axillary branches, the process

is repeated and the axis is

multipodial,e.g., Viscum.

3

33 3

3

333 3

2

(^22)
(^33)
333
3
2
1
44 34
3
4 2 2
4 4
3
(^34)
Multiparous
Further growth is continued by a
whorl of three of more axillary
branches.The axis is multipodial,
e.g., Euphorbia helioscopia.
Buds

• Stem grows by means of a terminal bud which represents a condensed immature or embryonic shoot possessing a growing
  point. The buds are generally small in size. The largest bud is that of cabbage. According to their nature/structure, buds can
  be vegetative (form leafy shoots only), floral (reproductive buds that develop into flowers) or mixed (both vegetative
  and floral branches).

On the basis of

activity

On the basis of

position

Buds may become dormant for short or

long periods. They are usually covered

by protective scales having hair, waxy

coating or resin, e.g., Ficus, Calotropis.

Some buds become active as soon

as they are formed. They are usually

naked.

Normal bud

Grow terminal

or lateral

Adventitious bud

Grow from position other than normal

Apical bud

Borne at apex

Lateral bud

Borne other than apices

Axillary bud

Arises in axil

of leaf, e.g.,

sunflower

Accessory bud

Arises on side or

above axillary bud,

e.g., Cucurbita

Extra-axillary bud

Arises on node, e.g.,

Solanum nigrum

Epiphyllous bud

Arises on leaves, e.g.,

Byrophyllum

Cauline bud

Arises on stem,

e.g., rose

Radical bud

Arises on roots, e.g.,

Ipomoea batatas

Types of Bud

Active

Dormant

Diverse Forms of Stem

• Stem may be aerial, sub-aerial or underground. These are variously modified to perform different functions such as storage
  of food, vegetative propagation, mechanical support, protection, etc.

Aerial stem

• Aerial stems are usually upright and may be erect or weak.