Remix education
AgricultureB.S.C

A Study of Stem and Their Modifications

by Fenee Patel02575

Exercise: 3A
Study of Stem and Their Modifications

Stem: It is the axis of a plant bearing leaves with buds in their axils. It is formed from the elongation of plumule of the seed.
ï‚· It is negatively geotropic,, positively phototropic and negatively hydrotropic
ï‚· It is generally green, with buds, nodes, iternodes, leaves, branches, flowers and fruits
Function:
ï‚· Supports branches, leaves, flowers and fruits
ï‚· Helps in conduction of water and food material through xylem and phloem
ï‚· Green stems synthesize food
ï‚· Store food in modified as well as normal structures
ï‚· Protects vegetative parts and helps in propagation

Different types of plants according to stem structure (Figure 3A.1):
Acaulescent: A plant which is stemless or without visible stem; onion, garlic
Arborescent: A plant almost tree-like with a short main trunk; Australian grass tree
Arboreous: A tree with well-developed trunk; mango, jackfruit
Culm: A jointed stem with distinct nodes and internodes; grasses and sedges

Plant types according to stem structure Arborescent Scape/ Acaulescent Culm Here are different types /Forms of stems according to habits, as below: Erect (Strong) Weak (cannot stand erect) 1. Herb (Succulent stem): Low, soft or coarse plant with annual stems (Figure 3A.2) Types according to structure i. Scape/Acaulescent: Shoot in 1. Creepers Herbaceous, spreads over a large surface area with daughter plants from different generations; Cynodon dactylon, Ipomoea batatas, Hydrocotyle asiatica(Figure 3A.2)

reproductive season only, without visible stem; onion, garlic ii. Creeper: Creeps over a large surface area for vegetative reproduction, roots arise at nodes; grasses, Strawberry, Oxalis iii. Culm: Solid nodes and hollow internodes - grasses Types according to duration of life i. Ephemerals (Lives for few weeks); Cannabis, Cardamine ii. Annuals (Lives for one season in a year); rice, wheat iii. Biennials/Biannuals (Lives for two years); parsley, fennel, hollyhocks iv. Perennials (Lives for more than two years); banyan, fig 1. Trailers (Prostrate – trails over surface) (Figure 3A.2) i. Procumbents: Lie flat; Basella, Evolvulus, Tribulus ii. Decumbents: For some length grow horizontally then straighten up; Portulaca, Lindenbergia iii. Diffuse: Profuse branches in all directions; Boerhaavia 3. Climbers (Climbs up support) (Figure 3A.3) i. Twiners/Stem climbers: Weak stems twine around support through specific movement (nutation); Clitoria ternatea, Convolvulus, Mikania scandens, Asparagus sp., Dolichos sp., Phaseolus sp. ii. Tendril climbers: Climbs through specialized structures called tendrils; Pisum sativum, Clematis sp., Gloriosa sp., Antigonon sp. a. Leaf, Lathyrus b. Stem apex or axillary branch, Vitis and Passiflora c. Petiole, Clematis d. Leaf tip, Gloriosa e. Inflorescence axis, Antigonon iii. Root climbers: Adventitious roots act as holdfast to climb support; Betel vine (Piper betle), Piper longum, Scindapus, Cuscuta iv. Scrambler/Rambler/Struggling plants & Hook climbers: Grow over other bushes with help of prickles, hooks, but do not climb; Rose, Calamus (Cane), Lantana, Carissa, Bougainvillea v. Adhesive climbers: The climbing organs have adhesive discs; Ampelopsis, Ficus repens vi. Lianas: Perennial, grow deep forest; Bauhinia, Ficus, Tinospora 2.Woody herbs/Undershrubs Structurally in between herbs and shrubs; Lilac 3. Shrubs: Larger than herbs, smaller than trees, much branching, bushy appearance, no main trunk, woody branches, perennial; Rose (Rosa), China – rose 4. Trees: Biggest plants, woody trunks, perennial, there are three types: i. Caudex: No branch, columnar; Palm trees ii. Excurrent: Indefinite acropetal branching; Pines, Casuarina, Polyalthia iii. Deliquescent: Spreading branching habits, Banyan (Ficus, Mango (Mangifera)

Plant types according to habits Herb Creeper Procumbent Decumbent Twiner Shrub Undershrub

Caudex Excurrent Deliquescent Figure 3A.3 Different climbers Tendril Climbers Hook climber Root climber Adhesive climber Liana

Figure 3A.4 Stem branching types Biparous cyme Trichasium Racemose branching Uniparous scorpiod cyme Uniparous helicoids cyme Dichotomy Helicoid dichotomy Scorpioid dichotomy Branching of stems: Branches develop from axillary buds (Figure 3A.4): Lateral/Axillary (arise from lateral buds) 1.Racemose/Monopodial: Lateral buds arise acropetally, single axis, grows indefinitely; Polyalthia, Casuarina, Alstonia Dichotomous: Typical branching of Cryptogams 1. Normal dichotomy: Apical cell/cells

2.Cymose: Apical bud lost with development, limited vertical growth, spreading type, Shorea Robusta a.Uniparous cyme – One strong branch i. Scorpioid cyme: Successive branches arise alternately at right and left, straighten up, forms false axis called pseudopodium; Vitis (Grapes) ii. Helicoid cyme: Successive branches arise alternately at one side only, straighten up, forms pseudopodium; Saraca indica b. Biparous cyme: Two strong branches, develops asymmetrical shoot – Dichasium, appear as dichotomy, hence named False Dichotomy; Plumeria acutifolia, Carissa carandas, Mirabilis jalapa c. Multiparous cyme: More than two strong branches, develops asymmetrical shoot – Trichasium (Nerium odorum), polychasium (Croton sparciflorus) bifurcate giving rise two apical branches; pteridophytes 2. Sympodial dichotomy: Sometimes after bifurcation one half grows and the other is suppressed. Here also two types are there: a. Scorpioid: alternate suppression on left or right branching; Male shield fern b. Helicoid: Suppression of cells of one side only; Pteris Modification of stem: Some stems are modified to fulfil different physiological functions as described below: Underground modification Purpose: Vegetative propagation, Perennation, storage (Figure 3A.5) Sub-aerial modification Purpose: Vegetative propagation, Perennation (Figure 3A.6) Aerial modification Purpose: Vegetative propagation, Perennation (Figure 3A.7) 1.Rhizome: Fleshy and horizontal brown stem below soil, small nodes and internodes covered with scaly leaves; Ginger (Zinziber officinalis), Turmeric (Curcuma longa), Canna, Water lily, Banana (Musa) Rootstock: Special rhizome with vertical stem, Alocasia indica 2.Stem tuber: Swollen tips of underground branches under soil, axillary buds called eyes covered with scaly leaves; Potato (Solanum tuberosum) , 1.Runner and sobole: Special branches of creepers carry buds, buds develop into daughter plant at a distance after internodes elongate horizontally, get fixed into soil through adventitious roots; Cynodon dactylon (Doob grass), Oxalis, Hydrocotyle asiatica 2. Stolon: Special runner, grow vertically then bend down to soil and develop roots; Mentha, Fragaria (Wild strawberry), Jasmine; Method used 1. Phylloclade/Cladophyll : Green photosynthetic flattened/ rounded succulent stem, leaves feebly developed or modified into spines to reduce transpiration, a kind of desert adaptation; Opuntia, Casuarina, Euphorbia, Cactus 2. Cladode: Phylloclades with single internode; Asparagus, Ruscus 3. Thorn: Axillary bud modified into thin hard structures; Bougainvillea, Duranta,

Helianthus tuberosus 3.Bulb: Underground modified bud with reduced stem as disc, fleshy storage scale leaves, there are two types, as below, a. Tunicated:Scale leaves arranged concentrically, Onion b. Scaly/Imbricate: Scaly leaves arranged loosely, Garlic 4.Corm: Condensed vertical rootstock, large apical bud, spherical node and inter node; Colocasia, Alocasia, Amorphophallus, Saffron, Gladiolus, Colchicum in layering of fruit tress 3. Sucker: Underground runner, branches develop obliquely from nodes above the soil; Mentha arvensis, Pineapple, Chrysanthemum 4. Offset: Thicker and shorter runners of aquatic plants, nodes bear rossette of leaves, tuft of roots at base; Pistia, Eichhornia Acacia, Carissa 4. Stem tendril: Spirally coiled modified buds of climbers; Passiflora, Vitis 5. Bulbils: A condensed , fleshy axillary flower buds; Dioscorea, Globba, Agave, Oxalis 6. Thalamus: Floral axis; all flowers 7. Pseudobulb: Fleshy, tuberous internodes; Many orchids 8. Dwarf shoot/Spur/ Brachyplast: Special secondary stems bearing more foliage leaves than main stem with close internodes; Berberis, Many gymnosperms Figure 3A.5 Underground modifications of stem Rhizome Root stock Stem tuber Corm

Tunicated bulb Imbricate bulb Figure 3A.6 Sub aerial modifications of stem Runner Stolon Phylloclade Suckers Offset Figure 3A.7 Aerial modifications of stem Dwarf shoot Cladode

Tendril Bulbil Thalamus Thorn Pseudobulb

Questions
1. Define:
i. Shoot system ii. Acaulescent iii. Arborescent iv. Arboreous v. Culm
2. Enlist different types of stem modifications with function and proper examples.
3. Write down the important functions of stem.
4. Differentiate between
a. Stem and root b. Culm and Caudex c. Strong and weak stems
d. Thorn and prickles e. Underground and aerial modification of stem
5. What are the main types of plants according to habit.
6. Draw neat and labeled diagram of angiospermic plant.