STEM AND ITS MORPHOLOGY

STEM AND ITS MORPHOLOGY

The stem arises from plumule and bears leaves, branches and flowers. It is generally erect, strong and negatively geotropic. Stems are differentiated into regions called Nodes. The distance between two nodes is called Internodes. Nodes give rise to branches and leaves. The growing apex of the stem is covered by numerous, tiny developing leaves called Apical Bud. The buds that arise from the axil region is called as Axillary Bud. Therefore the definition of the stem goes as A stem is the main ascending axis of a plant which develops from the plumule and epicotyl of the embryo. In flowering plants, it bears leaves, branches, flowers and fruits. It has nodes and internodes which distinguish it from other plant parts even if it happens to be an underground stem”.



SALIENT FEATURES AND FUNCTIONS OF A STEM

SALIENT FEATURES OF STEMFUNCTIONS OF STEM
NEGATIVELY GEOTROPIC AND POSITIVELY PHOTOTROPIC.SUPPORT.
AN ASCENDING AXIS DEVELOPS FROM PLUMULE AND EPICOTYL OF AN EMBRYO.STORAGE.
DIFFERENTIATED INTO NODES AND INTERNODES.SYNTHESIS OF FOOD.
APEX BEARS TERMINAL BUD FOR GROWTH IN LENGHT.PERENNATION .
YOUNG STEM IS GREEN MAY PERFORM THE FUNCTION OF PHOTOSYNTHESIS.VEGETATIVE PROPAGATION.
HAIRS IF PRESENT ARE MULTICELLULAR.PROTECTION.

CLASSIFICATION OF STEM BASED ON STRENGTH, HEIGHT AND LIFE SPAN

CLASSIFICATION BASED ON STRENGTH AND HEIGHTCLASSIFICATION BASED ON LIFE SPAN
HERBS-SMALL PLANT WITH SOFT STEM. EXAMPLE- GROUNDNUT.ANNUALS-PLANTS COMPLETE THEIR LIFE CYCLE IN ONE SEASON.
EXAMPLE- RICE.
SHRUBS- MEDIUM-SIZED PLANT WITH WOODY STEM THAT BRANCH PROFUSELY FROM THE BASE AND ATTAINS A BUSHY APPEARANCE.
EXAMPLE- COTTON.
BIENNIALS-PLANTS COMPLETE THEIR LIFE CYCLE IN TWO SEASONS.
EXAMPLE- RADDISH.
TREES- THEY HAVE STOUT AND TALL TRUNK WITH PROFUSE BRANCHING.-EXAMPLE- MANGO.PERENNIALS- PLANTS WHICH SUVVIVE FOR A NUMBER OF YEARS AND PRODUCE FLOWERS AND FRUITS.
EXAMPLE- MANGO.


DIFFERENT FORMS OF STEMS

UNDERGROUND STEMSUB-AERIAL STEM
THE STEMS OF SOME PLANTS REMAIN IN THE GROUND AND SERVE THE FUNCTION OF PERENATION AND STORAGE OF FOOD.IN SOME PLANTS, BRANCHES ARE WEAK, LIE PROSTRATE ON THE GROUND OR MAYBE BURIED IN THE TOPSOIL. THEY DEVELOP THE ADVENTITIOUS ROOTS AT THE NODES. AN INDEPENDENT PLANT MAY BE OBTAINED BY DETACHING AN ENTIRE BRANCH OR NODE. SUCH PLANTS ARE CALLED CREEPERS.
TYPES OF UNDERGROUND STEMSTYPES OF SUB-AERIAL STEMS
RHIZOMES- THEY AREPROSTRATE AND THICKENED STEMS THAT GROW HORIZONTALLY IN THE GROUND. NODES ARE MARKED AS SCARS, BEARS SCALE LEAVES WITH BUDS ON BRANCHES IN THEIR AXILS. THEY PRODUCE ADVENTITIOUS ROOTS.-EXAMPLE-GINGER.RUNNERS-STEM WITH LONG INTERNODES RUNNING HORIZONTALLY ON THE SURFACE OF THE SOIL. ROOTS ARE GIVEN OUT AT NODES. AXILLARY BUD FORMS A NEW AERIAL SHOOT.-EXAMPLE- OXALIS.
BULBS- IT IS CHARACTERISED BY THE PRESENCE OF HIGHLY CONDENSE AND DISCOIDAL STEM AND A LARGE NUMBER OF FLESHY SCALES. A CLUSTER OF ADVENTITIOUS ROOTS AT THE BASE. THE TERMINAL BUD AT THE CENTRE GIVE RISE TO A NEW PLANT.-EXAMPLE-GARLIC.SUCKERS-THEY ARE LIKE RUNNERS BUT ORIGINATED FROM THE BASAL AND UNDERGROUND PORTION OF THE MAIN STEM. IT IS SHORTER AND STOUTER THAN RUNNERS. EXAMPLE- CHRYSANTHEMUM.
CORM-THE SWOLLEN BASE OF AN UNDERGROUND STEM AXIS, ENCLOSED BY DRY, SCALE LIKE LEAVES. THE DIFFERENCE BETWEEN THE BULB AND THE CORM IS THAT CORM HAS GREAT AMOUNT OF STEM TISSUE WITH DISTINCT NODES AND INTERNODES.-EXAMPLE-COLOCASIA.STOLON-STOLON IS A SLENDER LATERAL BRANCH THAT ARISES FROM THE BASE OF MAIN AXIS. THEY GROW AERIALLY AND THE BRANCHES ARCHES DOWNWARD TO TOUCH THE GROUND WHERE TERMINAL BUD GIVE RISE TO A NEW SHOOT AND ROOT.-EXAMPLE- JASMINE.
TUBER- THE MODIFIED STEM WHICH DEVELOPS UNDERGROUND BY SWELLING OF TIPS OF A STEM. IT STORES A LARGE AMOUNT OF RESERVE MATERIALS MAINLY STARCH. THE ‘EYE’ PRESENT ON THE SURFACE OF POTATO REPRESENTS NODE.- EXAMPLE-POTATO.


MODIFICATIONS OF STEMS

MODIFICATION FUNCTION
TENDRILTHEY ARE SLENDER AND SPIRALLY COILED STRUCTURES AND HELP PLANTS IN CLIMBING.-EXAMPLE-GRAPES.
THORNSTHE AXILLARY BUDS DEVELOP INTO WOODY, STRAIGHT AND POINTED STRUCTURES THEY ARE CALLED AS THORNES. THEY MAY HAVE LEAVES. THEY PERFORM THE FUNCTION OF PROTECTION FROM BROWSING ANIMALS.-EXAMPLE- BOUGAINVILLAEA.
PHYLLOCLADESTHE PLANTS OF ARID REGION HAVhttp://successsamrat.com/E FLESHY, CYLINDRICAL OR FLATTENED STEMS. THEY CONTAIN CHLOROPHYLL AND PERFORM THE FUNCTION OF PHOTOSYNTHESIS. THEY HAVE SEVERAL NODES AND INTERNODES AND LEAVES ARE REDUCED TO SPINES.
CLADODETHEY ARE PHYLLOCLADE WITH ONE OR TWO INTERNODES ONLY. IT RESEMBLES A LEAF. IT ARISES IN THE AXIL OF A MUCH REDUCED SCALE LEAF.-EXAMPLE-ASPARAGUS.

Madhvendra Mishra

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