Epidermis. The transverse section of a typical young dicotyledonous stem shows that the epidermis is the outermost protective layer of the stem. Covered with a thin layer of cuticle, it may bear trichomes and a few stomata.
Cortex. The cells arranged in multiple layers between epidermis and pericycle constitute the cortex. It consists of three sub-zones. The outer hypodermis, consists of a few layers of collenchymatous cells just below the epidermis, which provide mechanical strength to the young stem. Cortical layers below hypodermis consist of rounded thin-walled parenchymatous cells with conspicuous intercellular spaces. The innermost layer of the cortex is called the endodermis. The cells of the endodermis are rich in starch grains and the layer is also referred to as the starch sheath. Pericycle is present on the inner side of the endodermis and above the phloem in the form of semi-lunar patches of sclerenchyma. In between the vascular bundles, there are a few layers of radially placed parenchymatous cells, which constitute medullary rays

Vascular Bundles. A large number of vascular bundles are arranged in a ring; the 'ring' arrangement of vascular bundles is a characteristic of dicot stem. Each vascular bundle is conjoint, open, and with endarch protoxylem. A large number of rounded, parenchymatous cells with large intercellular spaces which occupy the central portion of the stem constitute the pith.
Differences between dicot and monocot stems

A tissue is a group of cells having a common origin and usually performing a common function.
Simple Tissues. A simple tissue is made of only one type of cells. Simple tissues are of following types:
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma

Parenchyma. Parenchyma forms the major component within organs. The cells of the parenchyma are generally isodiametric. They may be spherical, oval, round, polygonal or elongated in shape. Their walls are thin and made up of cellulose. They may either be closely packed or have small intercellular spaces.
Function. The parenchyma performs various functions like photosynthesis, storage, secretion.
Collenchyma. The collenchyma occurs in layers below the epidermis in dicotyledonous plants. It is found either as a homogeneous layer or in patches. It consists of cells which are much thickened at the corners due to a deposition of cellulose, hemicellulose and pectin. Collenchymatous cells may be oval, spherical or polygonal and often contain chloroplasts. These cells assimilate food when they contain chloroplasts. Intercellular spaces are absent.
Function. They provide mechanical support to the growing parts of the plant such as young stem and petiole of a leaf.
Sclerenchyma. Sclerenchyma consists of long, narrow cells with thick and lignified cell walls having a few or numerous pits. They are usually dead and without protoplasts. On the basis of variation in form, structure, origin and development, sclerenchyma may be either fibres or sclereids. The fibres are thick-walled, elongated and pointed cells, generally occurring in groups, in various parts of the plant. The sclereids are spherical, oval or cylindrical, highly thickened dead cells with very narrow cavities (lumen). These are commonly found in the fruit walls of nuts; pulp of fruits like guava, pear and sapota; seed coats of legumes and leaves of tea.
Function. Sclerenchyma provides mechanical support to organs.

Dorsiventral (Dicotyledonous) Leaf : The vertical section of a dorsiventral leaf through the lamina shows three main parts, namely, epidermis, mesophyll and vascular system.
Epidermis. The epidermis which covers both the upper surface (adaxial epidermis) and lower surface (abaxial epidermis) of the leaf has a conspicuous cuticle. The abaxial epidermis generally bears more stomata than the adaxial epidermis. The latter may even lack stomata.
Mesophyll. The tissue between the upper and the lower epidermis is called the mesophyll. Mesophyll, which possesses chloroplasts and carry out photosynthesis, is made up of parenchyma. It has two types of cells - the palisade parenchyma and the spongy parenchyma. The adaxially placed palisade parenchyma is made up of elongated cells, which are arranged vertically and parallel to each other. The oval or round and loosely arranged spongy parenchyma is situated below the palisade cells and extends to the lower epidermis.

There are numerous large spaces and air cavities between these cells. Vascular system. This includes vascular bundles, which can be seen in the veins and the midrib. The size of the vascular bundles is dependent on the size of the veins. The veins vary in thickness in the reticulate venation of the dicot leaves. The vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.

(i)

(ii) 

The arrangement of ovules within the ovary is called placentation.
It is the following types
(i) Marginal  The placenta forms a ridge along the ventral suture and ovules are borne on the ridge,
e.g., pea, bean etc
(ii) Axile The margins of the carpels fuse to form a central axis on which the ovules are attached.
e.g., Hibiscus, Citrus, etc.
(iii) Parietal The placnta develops on the ovary wall,
e.g., Cucurbita.
(iv) Basal The placenta arises from the base of the unilocular ovary and bears a single ovule,
e.g., sunflower
(v) Free-Central The ovules are borne on central axis and septa are ansent, e.g., primrose.

The mode of arrangement of leaves on the stem and its branches is called phyllotaxy (Phyllon-leaf; taxis arrangement). They are arranged most systematically, regularly and mathematically, so as to get proper sunlight and avoid overcrowding.
Phyllotaxy in leaves is of following three types.
(i) Alternate: A single leaf arises at a node. e.g, China rose, mango, mustard, sunflower, etc.
(ii) Oppposite: Two leaves arise at a node,opposite to each other e.g, guava, Calotropis tulsi, etc.
(iii) Whorled: More than two leaves arise at each node forming a circle or whorl, e.g, Alstonia Scholaris etc.

These can be distinguished as follows

(a) Tendrils- Stems in weak plants provide support by coiling and climbing in the nearby structure. They are thin and slender. In cucumbers, melons and many other tendrils are seen. Tendrils help plants to climb on the support e.g cucumber
(b) Thorn- A spine-like structure is seen in plants like bougainvillea and is called thorn. These protect the plants from herbivorous animals. The thorns have a sharp and pointed structure. Thorns are woody pointed,straight structures to protect plants from browing animals e.g. Baugainvillea
(c) Fleshy stems In plants in arid regions modify stemsinto flattened or fleshy cylindrical structures. They contain chlorophyll and carry out photosynthesis.

The description of gynoecium in various plants.
(i) Carples Monocarpellary /bi carpellary/ tricarpellary/tetracarpellary /multi-capillary
(ii) Cohestion Apocarpous/Syncarpous
(iii) Overy Superior/semi-inferior/inferior.
(iv) Placentation Marginal/axile/parietal/basal/free-central/superficial.
(v) Style Terminal/lateral/gynobasic/stylopodium
(vi) Stigma number,shape-simpe,lobed,capitate,branched.

Fleshy stems In plants in arid regions modify stemsinto flattened or fleshy cylindrical structures. They contain chlorophyll and carry out photosynthesis.