Forms and Types of Stem
Forms of Stem:
- Strong Stem:
The following terms are important in relation to strong stems.
- Excurrent:- The main axis shows continues growth and the lateral branches develop regularly giving a conical appearance to the trees; Pinus.
- Deliquescent:- The growth of lateral branch is more vigorous than that of main axis. The tree has a rounded or spreading appearance; e.g. Mangifera, Ficus.
- Caudex:- It is unbranched, stout, cylindrical stem, marked with scars of fallen leaves; e.g. Cocos, Date-palm.
- Clum:- Erect stems with distinct nodes and internodes. Stem shows jointed appearance. e.g. Bambusa arundinacea.
Branching of stem
Stem branching is of three types:
- Dichotomous: Pandanus, Asclepias.
- Racemose (Monopodial): Pinus, Eucalyptus.
- Cymose: a) Sympodial or uniparous cyme. e.g., Saraca (Helicoid), Grape (Scorpoid).
b) Dichasial cyme: e.g. Viscum, Datura.
c) Polychasial cyme : e.g., Euphorbia, Croton.
Types of stem
Theses stems cannot maintain an upright position. Weak stems can be divided into following categories:
It is a weak stem that spreads over the surface of the ground without rooting at the nodes. These fall into three categories:
- Prostrate (procumbent): A stem that lies flat on the ground.
The plant grows horizontally on the ground and gives off roots at each node; e.g. grasses, strawberry, Oxalis. Runners, stolons, offset and suchers.
This week stem climbs a support by means of some special structure or organ for attachment. These are divided into following types.
- Twiners : It is week, long and slender stem that climbs by twining is body around the support.
- Tendril Climbers : It is a week stem climbing by its slender, leafless, spirally coiled structures, known as tendrils.
- Leaf tendril : The whole leaf is modified into a tendril.
- Leaflet tendril : Some upper leaflets of a leaf are modified into a tendril.
- Petiole tendril : Petiole is modified into a tendril e.g., Clematis.
- Leaf apex tendril : Apex of a leaf is modified into a tendril e.g. , Gloriosa.
- Stipule tendril : Stipule is modified into a tendril e.g., Smilax.
- Apical bub tendril : Apical bub is modified into a tendril e.g. , Vitis.
- Axillary bub tendril : Axillary bub is modified into a tendril e.g., Passiflora (Passion flower).
- Extra axillary bub terndril : e.g. cucurbits.
- Inflorescence axis tendril : Inflorescence axis is modified into a tendril e.g., Antionan.
- Root climbers : Such climbers give out adventitious roots at each node which stick to the support; e.g. Pothos scandens (money plant).
- Hook climbers (Scramblers) : In Bougainvillea.
- Lathyrus - Whole leaf modified into tendril
- Pisum sativum – Upper leaflet modified into tendril,
- Clematis – Petiole modified into tendril,
- Gloriosa – Leaf apex modified into tendril,
- Smilax – Stipule modified into tendril.
Sucker :- Arising from the basal underground portion of the main. Initially it grows horizontally below the surface of the earth but soon grows obliquely upward forming a leafy shoot e.g. Chrysanthemum.
It is subterranean long lateral branch arising from base of the stem. It first grows obliquely upward and then bends down to touch the ground surface. e.g., Colocasia.