Plant AnatomySEMESTER -06

Types of Stem In Dicots

StemDicotyledonous stemExternal Stem StructureTypes of StemHerbaceous Dicot stemWoody Dicot Stem

Stem❖ Stems are usually above ground organs andgrow towards light (positively phototropic)and away from the ground (negatively

geotropic), except in the case of certain

metamorphic (modified) stems.❖ Ranging from rope like Vines to massive Treetrunks.❖ Either Herbaceous or Woody.

External Stem Structure❖ Bud – A stem's primary growing point. Buds can beeither leaf buds (vegetative) or flower buds (reproductive). ❖ Terminal bud – Bud on end of a branch, where all ofnext years length (of branch) is added.

❖ Lateral buds grow from the leaf axils on the side ofa stem. ❖ Bud scales – A modified leaf protecting andcovering a bud ❖ Naked bud – Bud without a protective bud

scale;characteristic of the Viburnum family.

❖ Leaf scar – Mark left on stem where leaf was attached. Often used in woody plant identification.❖ Bundle scar – Marks left in the leaf scar from the vascular tissue attachment. Used in woody plantidentification.

❖ Lenticel – Pores that allow for gas exchange❖ Terminal bud scale scars or annual growth rings – Marks left on stem from the terminal bud scales inprevious years. Terminal bud scale scars are an external measure of annual growth.

❖ Node-Segment of stem where leaves andlateral buds are attached.

❖ Internode – Section of a stem between twonodes.

Types of DicotyledonousStems❖ Herbaceous Dicot Stem❖ Woody Dicot Stem

Herbaceous Dicot Stem❖ Stems with only primary growth

are herbaceous. ❖ e.g Young Sunflower stem

Internal Structure of Herbaceous Dicot Stem❖ Epiderm❖ The epidermis consists of a single layer of living cells which are closely

packed ❖ Cuticle ❖ Stomata ❖ Cortex❖ This region comprises the collenchyma, parenchyma and endodermis. It issituated to the inside of the epidermis.

❖ CollenchymaThese cells lie under the epidermis and constitute three to four layers of cells withcell walls thickened at the corners❖ ParenchymaBeneath the collenchyma cells are a few layers of thin-walled cells, parenchyma, withintercellular spaces❖ Vascular BundlesThe vascular bundles are situated in a ring on the inside of the pericycle of the plant.This distinct ring of vascular bundles is a distinguishing characteristic ofdicotyledonous stems

Epidermal hairs

Hypodспmis r �ਂ Fo Hypoems collen.chyma) తా - بٹیا!Parenchyma} Cortex

" ព្ Middle ألحكـ தி نتيجة HE ÈY–Resinous canal వ్రై� ԱԱrtՅ:X - - శ్రీ� o Vascular bundles

బ్రీ�Bundle caps Vascular

Metaxylem o Xylem fibre – Est Medullary rays ProtoxylernPith

Fig. 3.5.1 : T.S. of young dicot stem Fig. 3.5.2 : T.S. of young dicot stem(Sunflower) ground plan (Sunflower) - A sector enlarged

❖ Phloem fiber capPhloem contains a cluster of fiber towards the outside of vascular bundles.

❖ Pith (Medulla)The pith occupies the large central part of the stem. It consists of thin-walled parenchyma cells with intercellular air spaces. Between each vascular bundle is a band of parenchyma, the medullary rays, continuous with the cortex and the pith.

Woody Dicot Stem❖ Plants with primary and

secondary growth ❖ Flowering plant, all have dicot

stem ❖ E.g apple , maple

Internal Structure of Woody StemPrimary tissues in woody dicots are organised like those in herbaceous dicot stem.❖ Woody dicot stem has three distinct areasBark( cork, cork cambium and phloem)Wood (containing xylem)Pith .

❖ Vascular CambiumProduce secondary xylem and secondary phloem

As secondary xylem is deposited, the cambium continues to move outward. The cambium, being continuously enlarged, must make not only xylem and phloem, but also additional cambial cells.

sieve plates❖ The most prominent elements ofphloem are those that compose the sieve tubes. These elements are elongated cells arranged end to end and having perforated end walls.

❖ sieve-tube elements, havingcytoplasm, are living

Lenticels❖ Bark often possesses

openings ❖ to allow an exchangeof gases

Spring woodContains wide vessel elements

Summer WoodContains lower portion of wide vessel elements

Numerous fibers and thick walled trachieds.

Sapwood Heartwood Bark Herw000 andSepw000 -o-,

".o - Periderm

• HeartWOOdlies at the Center of Older ....

No. 7 | Cork cambium stems and roots. o con.

–It depository for resins, oils, gums and tannins o- o | -

– It makes tree Strong and able to defy gravityl | ||

| | .-

O SapW00d. is secondary growth located between heartwood and the Vascular

o o o ു�ണ - o ಗ್ಲಿ�..... m Wet pale in color and is not stong – Rich in the Sugar-

lich fluid of the phloem|

Wascular cambium

RefrencesBiologyBy Eldra Solomon, Linda Berg, Diana W. MartinCompetition Science Vision Nov 2004A Text Book Of botany: Plant Anatomy and Economic Botany, Volume 3By Pandey S N, S. N. Pandey, Ajanta Chadhhttp://www.biocyclopedia. com/index/introduction_to_botany/the_woody_dicot_stem.phphttp://www.botany.uwc.ac.za/sci_ed/grade10/anatomy/stemhttp://www. biologydiscussion.com/shoot-system/stems/dicotyledonous-stems/dicotyledonous- stems-regions-structure-and-types-botany/20424s.htm#top