Morphology of Flowering Plants-Defination and Modification of Stem

                     Morphology of Flowering Plants

Defination :-

The main body or stalk of a plant or woody plant, generally rising higher than ground however sometimes subterranean.

Stem

Origin of Stem :-

Origin of Stem

The first stem plant tissue is organized throughout the event of the embryo.

 The absolutely developed embryo usually consists of AN axis, the hypocotyl-root axis.

 The axis bears at its higher finish, one or a lot of cotyledons and therefore the shoot anlage, whereas at its lower finish it bears the foundation anlage lined with a root-cap.

The anatomical structure (embryonic root) is found at the lower finish of the hypocotyl and therefore the embryonic shoot is found higher than the insertion of the cotyledons. 

The embryonic shoot consists of AN axis bearing un-extended internodes and one or a lot of leaf primordia. 

This shoot (first bud) is usually called down feather and its stem half is termed epicotyl.

Internal Structure :-

Internal Structure of Stem

Epidermis :-

 it's the outmost uniseriate zone, consisting of tabular cells atta¬ched endways finish while not going living thing areas.

 The cells live with cavum body part. The chloroplasts area unit sometimes absent.

 Cortex:-

 It happens next to cuticle and represents the extrastelar ground tissues. In helianthus stem cortex is differentiated into 3 zones. simply internal to cuticle there area unit some layers of collenchyma, sometimes angular ones, forming

 Stele:-

All the tissues occurring internal to the starch sheath represent the stele. it's a compound siphonostele, consisting of tube-shaped structure bundles organized in kind of a hoop, and intrastelar ground tissues.

Vascular bundles:-

The tube-shaped structure bundles square measure usually collateral and open ones, with vascular tissue and bast on an equivalent radius, vascular tissue being internal and bast external. 

A strip of lateral plant tissue, cambium, is gift between vascular tissue and bast.

The vascular tissue is characteristically endarch, showing centrifugal mode of differentiation from the procambium.

Pericycle :-  

This layer is placed in between the endodermis and tube-shaped structure bundles.

 The perieycle of stem is multilayered and created of  sclerenchyma. Sclerencymatous perieyle is additionally called laborious bast.

Against each vascular tissue there's a patch of sclerenchyma forming one thing sort of a cap. This has been referred to as bundle cap. 

The patches of sclerenchyma and intervening parenchyma cells were thought-about to represent the peri-cycle, the outer portion of the stele.

But trendy employees square measure of opinion that the fibres related to the vascular tissue in helianthus stem, and as a matter of truth, in several different plants, belong to bast.

 that the term laborious bast has conjointly been attributed to the present patch. an entire section shows that the bundles square measure settled towards the bound and therefore the massive central portion remains occupied by parenchyma cells with pro¬fuse living thing areas. 

This half is thought as pith or medulla.

Modifications of Stem :-

1. For food storage: 

E.g. underground stems of potato, ginger, turmeric, zaminkand, liliopsid genus etc.

Also act as organs of perenation.

2. Stem tendrils: 

Stem tendrils

Slender and spirally convolute structures developed from axillary buds.

 Help

plants to climb. E.g. Gourds (cucumber, pumpkins, watermelon) and grapevines.

3. Thorns: 

Tendrils and Spines

Woody, straight and pointed structures developed from axillary buds. defend the plants

from browsing animals. E.g.,Citrus, vine.

4. Phylloclade: 

inexperienced, planate or fleshy cylindrical stem containing chlorophyl for

photosynthesis. Found in some plants of arid regions. E.g. genus Opuntia (flattended stem), Euphorbia (cylindrical stem).

5. Stolon:-

A slender lateral branch that arises from the bottom of the most axis and when growing

aerially for a few time arch down to the touch the bottom. E.g. plants like mint .

6. Offset:-

Eichornia And Pistia

 A lateral branch with short internodes and every node bearing a rosette of leaves and a

tuft of roots. E.g. aquatic plants like Pistia stratoites and liliopsid genus.

7. Sucker:- 

The lateral branches that originate from the basal underground portion of the most

stem. It grows horizontally at a lower place the soil and are available out obliquely upward giving rise to foliaged shoots. E.g. Banana, Pineapple and Chrysanthemum. 

Underground stems of some plants (e.g. Grass and Strawberry) unfold to new niches and once older elements die new plants square measure shaped.