Depending upon the size and woodiness of plants, they are classified as
1. Herbs: These are plans with soft stem eg. Brassica (mustard), Raphanus sativus (Raddish), Triticum vulgare (wheat)
2. Shrubs: Medium-sized woody stems that braches profusely and attain a busing appearance. eg. Hibiscus rosa sinensis.
3. Trees: These have a stout and tall trunk with profuse branching. eg. mango, sisham.

· Stem arises from the plumule of the embryo, whereas roots from the radicle.
· Normally bears leaves, branches, and flowers.
· Bears multicellular hairs.
· Provided with nodes and internodes, which may not be distinct in all cases.
· Leaves and branches arise from nodes.
· Normally stem is negatively geotropic but positively phototropic.
· Stem may be aerial or underground and green stems carry out photosynthesis.
· Acts as an organ of perennation, i.e. surviving year after year through unfavourable conditions in certain underground stems.

Various Modifications of Stem

A. Underground stem:
· Underground stem serves as an organ of perennation and food storage.
· They have scaly leaves, nodes and internodes and they also have axillary and terminal buds.

a. Rhizome
· A thick, fleshy, Prostrate stem grows horizontally.
· Nodes, internodes, and scale leaves are distinct.
· It gives out a number of adventitious roots from the lower side.
· Has a terminal and axillary bud. 
· E.g. Ginger (Zingiber officinale). Curcuma domestica (Turmeric), Banana, Water lily etc.

b. Tuber
· Swollen terminal portion of an underground lateral stem (stolon) that stores a large amount of food material in the form of starch.
· The eyes of potatoes are the buds that develop at the nodes.
e.g. Potato (Solanum tuberosum)

c. Bulb
· It has a short flattened disc-like stem with a number of scaly leaves.
· Food is stored in these scaly leaves.
· The outer one is dry and the inner ones are fleshy which enclose terminal buds.
· Tunicated bulb is covered with a sheath.
· E.g. Simple tunicated – Onion (Allium cepa)
Compound tunicated – Garlic (Allium sativum)

d. Corm
· A short underground vertical fleshy solid stem, which serves for the storage of food.
· Several dry, thin scaly leaves with distinct nodes and internodes enclose the stem.
e.g. Colocasia (Pidalu), Amorphyllus, Colchicum autumnale, Crocus.

B. Subaerial stems

· They are basically for the purpose of vegetative propagation.
· They are found in the plants with weak stems in which branches lie horizontally on the ground. A part of the stem gets buried in the soil and a part above the ground.
· Aerial branches and adventitious roots develop at the node. Such plants are also called creepers.

a. Runner
· It is a long thin green stem with long internodes growing horizontally on the soil surface.
· It arises as an axillary bud, which creeps some distance away from the parent plants, gives out roots at nodes and the axillary buds form a new shoot.
e.g. Strawberry (Fragaria), Oxalis (wood-sorrel), Centella, Cynodon (dubo grass)

b. Stolon
· Weak slender lateral branch arises from the base of the stem.
· After growing aerially for sometimes stem bends downwards and touches the ground where its terminal bud gives rise to a new shoot and roots. 
· E.g. Jasmine (Jasminum), wild strawberry (Fragaria indica)

c. Offset
· A short, thick, horizontal branch, develops from the axis of the leaf which elongates to some extent only.
· The apex produces a bunch of leaves above and a cluster of roots below the ground.
· E.g. Water lettuce (Pistia), Water hyacinth (Eichhornia)

d. Sucker
· Originate from the basal underground portion of the main stem and grows obliquely upwards and gives rise to a leafy shoot or a new plant.
· E.g. Chrysanthemum, Rose, Mint, Banana, pineapple etc.

Fig: Subaerial Modification of Stem

Weak stems
Creepers: These plants creep on the ground bearing roots at the nodes eg. grasses.
Trailers: Plant grow prostate and spread over the field but roots are not formed at nodes. eg Portulaca.
Climbers: Plants with special structures which help in climbing e.g. Root climbers (eg. Pothos, Piper), Tendrils (eg. Smilax), Cinetum.

C. Aerial modifications
· Vegetative and floral buds normally develop into branches and flowers respectively.
· They often undergo an extreme degree of modification (metamorphosis)

a. Tendrils
A. Stem tendrils – Modified axillary branch, e.g. Passiflora
B. Extra axillary Branch tendril. e.g. Cucurbita
C. Branch tip tendril. e.g. grape, vine
Leaf tendrils
· Whole leaf tendril: Lathyrus aphaca (wild pea)
· Leaflet tendril: Lathyrus odoratus (sweet pea), Pisum sativum (garden pea)
· Leaf tip: e.g. Gloriosa
· Petiole tendril: e.g Pitcher plant, (Nepenthes)
· Stipular tendril: e.g. Smilax

b. Thorn
· Modified stem or axillary bud.
· The thorn is a defensive organ meant to keep off browsing animals.
· Also used as a climbing organ. e.g. Bougainvillea (Glory of the garden)

c. Spine
· These are the modified leaf that acts as the defensive organ in a plant. e.g. Climbing Asparagus

d. Prickles
· Not modification of any morphological organs.
· Mostly defensive organ.
· No vascular supply
· Usually curved which are commonly used for climbing.
e.g. Climbing Rose (Rosaceae)

e. Phylloclade
· Green, flattened or cylindrical stem or branch of unlimited growth consisting of a succession of nodes and internode at long or short intervals.
· They are modified stem
· These are found in xerophytic plants growing in arid regions having a shortage of water.
· They carry out photosynthesis and store water for plants.
    1. Flattened phylloclade: Opuntia, Muehlenbeckia (Cocoloba)
    2. Cylindrical phylloclades: eg. Casuarina, Euphorbia.

f. Cladode/Cladophyll
· Short green cylindrical or flattened branch often resembling a leaf.
· It has limited growth and helps in photosynthesis.
· Found in xerophytes.
· Actually, cladode is a phylloclade with one or two internodes only.
· E.g. Asparagus, Ruscus (Butcher's brooms)

g. Bulbil
· Maybe the modification of vegetative or reproductive buds.
· It is a multicellular reproductive body, i.e. It is essentially meant for the reproduction of plants.
· On being shed from mother plant it grows up into a new independent plant
e.g. Agave, Dioscorea, Oxalis (wood-sorrel)

· Reduced stem – Stem is in the form of a small green disc, e.g. Radish, Carrot etc.
· Erect stem – Generally herbs, shrubs and trees have well developed mechanical tissue so they have an erect stem.
· Weak stems – There are several plants in which the stem is weak, and it cannot stand upright.
· Prostrate – Stem lies flat on the ground e.g. Portulaca.
· Twiners – Stem twins around the support without forming any special organ of attachment. E.g. Ipomoea, Dolichos, Convonvulus.
· Climbers – Attaches itself to the support with the help of special devices.
a. Root climbers – with the help of adventitious roots climbers attach to the support
e.g. Betel, Ivy
b. Scramblers – climbing with the help of hard structures such as
a. Prickles - e.g climbing rose
b. Spines - e.g climbing asparagus
c. Curved thorns - eg. Bougainvillaea
d. Lianas – woody climbers. e.g. Bauhinia

· Spines, prickles and bristles are the defensive organs of plants that protect them from excessive transpiration and grazing.
· Foliar buds: develop into vegetative parts.
· Floral buds: develop into reproductive parts.
· Mixed buds: develop both vegetative and reproductive parts.

Fig: Arial Stem Modification

Table To know (You can not afford to Skip this Golden Table !!!)

Underground Stems Subaerial Stems Aerial Stems
Example: Zingiber officinale
Example: Oxalis
Example: passiflora
Example: Solanum tuberosum
Example: Eichhornia
Example: Carrisa
Example: Amorphophallus
Example: Colocasia
Example: Opuntia
Example: Allium cepa (Onion),
Allium sativum (Garlic)
Example: Chrysanthemum
Example: Asparagus
Example: Asparagus
Example: Agave

High Yeilding Points from STEM

1. Effect of gravity on stems:
  • Orthogeotropic: Parallel to the force of gravity
  • Diageotropic: Perpendicular to force of gravity
  • Paleogeotropic: Either acute or obtuse angle to force of gravity
  • Apogeotropic: No effect of Gravity

2. Types of Stem:
a. BULB:
  • Simple Tunicated: Bulblet absent, Onion
  • Compound Tunicated: Bulblets present, Garlic
b. Offset: Pistia, Eichornia, Agava (@ PEA)
c. Sucker: Musca, Mint, Chrysanthemum (@MMC)
d. Corm: Crocus, Colocasia, Colchicine, Amarphophallous, Gladiolus
e. Bulbil: Agave and Dioscorea (@ Bad Bulbil)
f. Phylloclade: Euphoria, Opuntia, Mulehlenbeckia (@ MOE)
g. Phyllode: Perkinsonia, Australian Accasia

3. Modification of Tendril:
  • Termial bud tendril: Vitis (@ T.V)
  • Axillary bud tendril: Passiflora (@ bap)
  • Extra axillary bud tendril: Cucurbits
  • Leaf petiole modified to tendril: Nepenthes, Nastritium clematis (@ PNACLE).
  • Leaf stipule modified into tendril: Smilax
  • Leaf apex modified into tendril: Gloriosa
  • Floral bud modified into tendril: Antigonam
  • Leaflet modified into tendril: Lathyrus odoratus (Sweet pea) and Pisum sativum (garden pea) (@ Love sweet girl)

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