THE HON

leaves

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology.

Characteristics of leafUsualthin flattened organ borne above ground specialized for photosynthesis,

Sometimessome are not flat some are not above ground some are without major photosynthetic function

parts of leaf

Leaf blades differ from one another in several ways:

(1)the types of edges,

(2) the patterns of the veins,

(3) the number of blades per leaf.

The Blade, or lamina, is the broad, flat part of the leaf. Photosynthesis occurs in the blade, which has many green food-making cells.

Couple chain

Almost all narrow, grasslike leaves and needles leaves have a blade with a smooth edge, as do many broadleaf plants, particularly those that are native to warm climates.

The leaves of many temperate broadleaf plants have small, jagged points called teeth along the blade edge. Birch and elm trees have such leaves. The teeth of young leaves on many plants, including cottonwood and pin cherry trees, bear tiny glands.

Some temperate broadleaf plants -- including sassafras trees and certain mulberry and oak trees -- have lobed leaves. The edge of such a leaf looks as if large bites have been taken out of it. This lobing helps heat escape from the leaf.

The Types of Edges

vascular tissue of the leaf Veins carry food and water in a leaf. located in the spongy layer of the mesophyll The pattern of the veins is called venation.They also support the blade

The veins are made up of:

Xylem: tubes that bring water and minerals from the roots into the leaf. typically lies on the adaxial side of the vascular bundle

Phloem: tubes that usually move sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf. typically lies on the abaxial side.

The veins

.In most broad leaves, the veins form a netlike pattern, with several large veins connected by smaller ones. The smallest veins supply every part of the blade with water. They also collect the food made by the green cells.

There are two main types of net-vein patterns -- pinnate (featherlike) and palmate (palmlike or handlike). Pinnately veined leaves have one large central vein, called the midrib, which extends from the base of the blade to its tip. Other large veins branch off on each side of the midrib. The leaves of beech, birch, and elm trees have such a vein pattern. A palmately veined leaf has several main veins of about equal size, all of which extend from a common point at the base of the blade. The vein patterns of maple, sweet gum, and sycamore leaves are palmate.

Narrow leaves and needle leaves are not net-veined. Narrow leaves have a parallel-vein pattern. Several large veins run alongside one another from the base of the blade to the tip. Small crossveins connect the large veins. Needle leaves are so small that they have only one or two veins running through the center of the blade.

The Patterns of the Veins.

NETTED VENATION IS WHEN THERE ARE LARGER VEINS WITH MANY SMALLER VEINS BRANCHES MAKING A TYPE OF WEB PATTERN.IT IS FOUND IN DICOTYLEDONOUS PLANTS SUCH AS SANTOL, GUMAMELA ,ROSE, MANGO AND OTHERS

Netted venation

distribution or arrangement of a system of veins, as in a leaf blade or the

wing of an insect

LEAF VENATION MAY BE PARALLEL OR NETTED.

Leaf Venation

The Patterns of the Veins.

A leaf with only blade is called a simple leaf. Apple and oak trees, grasses, and many other plants have simple leaves. A leaf with more than one blade is known as a compound leaf. The blades of a compound leaf are called leaflets.

The Number of Blades per Leaf

The leaflets in a compound leaf may be arranged in a pinnate or palmate pattern. In pinnately compound leaves, the leaflets grow in two rows, one on each side of a central stalk, called the rachis. Plants with pinnately compound leaves include ash and walnut trees and garden peas. The leaflets in a palmately compound leaf all grow from the tip of the leafstalk. Clover, horse chestnut trees, and many other plants have palmately compound leaves.

A few plants -- including carrots, honey locust trees, and Kentucky coffee trees -- have double compound leaves, with each leaflet being divided into a number of still smaller leaflets. One double compound leaf looks more like a group of twigs and leaves than like a single leaf.

The Number of Blades per Leaf

The Petiolethe stemlike part of the leaf that joins the blade to the stem. Within a petiole are tiny tubes that connect with the veins in the blade. Some of the tubes carry water into the leaf. Others carry away food that the leaf has made. In many trees and shrubs, the petioles bend in such a way that the blades receive the most sunlight, thus assuring that few leaves are shaded by other leaves. The petiole also provides a flexible "handle" that enables the blade to twist in the wind and so avoid damage.

In some plants, the petioles are much larger than the stems to which they are attached. For example, the parts we eat of celery and rhubarb plants are petioles. In contrast, the leaves of some soft-stemmed plants, particularly grasses, have no petioles.

In some plants, the petioles are much larger than the stems to which they are attached. For example, the parts we eat of celery and rhubarb plants are petioles. In contrast, the leaves of some soft-stemmed plants, particularly grasses, have no petioles.

The Stipulesare two small flaps that grow at the base of the petiole of some plants. In some plants, the stipules grow quickly, enclosing and protecting the young blade as it develops. Some stipules, such as those of willows and certain cherry trees, produce substances that prevent insects from attacking the developing leaf.In many plants, the stipules drop off after the blade has developed. But garden peas and a few other kinds of plants have large stipules that serve as an extra food-producing part of the leaf.

Leaves are normally extensively vascularized and are typically covered by a dense network of xylem, which supply water for photosynthesis, and phloem, which remove the sugars produced by photosynthesis. Many leaves are covered in trichomes (small hairs) which have a diverse range of structures and functions.

serves several functions: protection against water loss by way of transpiration, regulation of gas exchange, secretion of metabolic compounds, and (in some species) absorption of water

Stomatais a pore, found in the leaf and stem epidermis that is used for gas exchange.

guard cells that are responsible for regulating the size of the opening

Cross section of a leaf.

Epidermal cells

Palisade mesophyll cells Spongy mesophyll cells

Basic types

Ferns have fronds Conifer leaves are typically needle-, awl-, or scale-shaped

Angiosperm(flowering plant) leaves: the standard form includes stipules, a petiole, and a lamina

Lycophytes have microphyll leaves

Sheath leaves (type found in most grasses)

Photosynthesis - [photo-], "light," and σύνθεσις [synthesis], "putting together", "composition") is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight

Photosynthetic functionTypically leaves are flat and

thin, thereby maximising the surface area directly exposed to light and promoting photosynthesis.

Occurs in photoautotrophs

External structure of leaves Petiole aka leafstalk ,is present in the leaves of most flowering

plants. It is a continuation of the stem to the rest of the leaf. sessile leaves w/out petiole are called sessile . The blade is

flattened , expanded portion of the leaf and is ususlly green. Some leafblade are needle-like as on pines , or scale like as cypresse.

Stipules some leaves have small leaflike stipules outgrowths at

the base of the petiole Midrib (lamina) this is the continuation of the petiole that runs at the

center of the leaf, it acts as the skeleton of the leaf and as paage of liquid substances bet. the petiole and the veins.

Veins it acts as the framework of the leaf . It distinguish a

monocot leaf from a a dicot leaf .

TYPES OF LEAVES1. Simple has single expanded portion

2.Compound a.) Bipinnately compoundLeafblade may be subdivided into everal separate expanded parts, or leafletsrachis~ extended portion ,a short stalk

b.) pinnately compounddescribes an arrangement of discrete structures arising at multiple points along a common axis.

THE LARGER VEINS ALL RUN THE LENGTH OF THE BLADE WITH SMALLER VEINS BRANCHING OFF

AND INTERCONNECTING THEM.

IT IS A CHARACTERISTIC OF MOST MONOCOTYLEDONOUS PLANTS , SUCH AS CORN ,ONION AND

COMMON GRASSES.

Parallel venation

phyllotaxythe arrangement of leaves on a plant stem (from Ancient Greek phýllon "leaf" and táxis "arrangement").

opposite leaf arrangement

two leaves arise from the stem at the same level (at the same node), on opposite sides of the stem. An opposite leaf pair can be thought of as a whorl of two leaves.

Alternate (spiral) pattern, each leaf arises at at different point (node) on the stem

whorl occur as a basal structure where all the leaves are attached at the base of the shoot and the internodes are small or nonexistent. A basal whorl with a large number of leaves spread out in a circle is called a rosette.