GENERAL STRUCTURE, ANATOMY, PHYSIOLOGY OF THE ROOT AND THE LEAF

Introduction

You have learnt the structure of the roots and the shoot. The shoot or the part above the ground is the structure which bears the leaves of a flowering plan. The leaves are the organ of photosynthesis. In this unit, you will study how some leaves are modified for certain function. You will study types of leaves, leaf venation, simple and compound leaves.

The Leaf

We have in the previous unit identified the leaf as one of the parts of a plant. You must have observed leaves of plants and note that the shape and size of these leaves are not the same. If you have not consciously done this before, just look critical at the leaves of different plants around you. Do you notice any difference among the leaves? We will now identify and classify leaves into the various types.

Types of Leaves

1. Leaf -tendrils: Just like the stem that develops as tendril, the leaf also possess this structure. They are tiny, slender structures that arise from the leaf apex, terminal leaflet. The plant climbs other objects by the sensitive tendrils coiling a or round the object e.g. of plants mith leaf-tendril are traveller joy, venus flower, glor y lily. 
2. Leaf -spine: Spines are like the thorn found on the stem of plant but might not be necessarily as sharp and strong as the thorns. Such leaves are modified as form of protection for the plant. These spines are found at apex of the leaf as in date-palm, leaf margin as in prickly poppy or the entire leaf is modif ied into spine as in barberry. The spine is called modif ied leaf because it develops from the point the leaf develops. 
3. Pitcher: The pitcher plant has its leaf modified into a sack like structure called linked to leaf by a tendril. The pitcher caputes and digest insects. 
4. Scale-leaves: These are fresh or dry leaves that protect mostly stems. Scale-leaves are found to protect the auxiliary buds. When they are thick underground and fresh as in onion, they store food and water but when dry they serve as protective cover. 
5. Bladder: Some plants like bladderwort, which float freely in water structures that look like bladder on its segmented body with an entrance through possess which any aquatic animal that enters can not come out again. 

 SIMPLE LEAF

A simple leaf is one that the leaf-blade runs from the apex of the leaf to the petiole. The petiole is attached to the stem. Now let us examine the different forms of compound leaves:

1. Pinnately compound Leaf: A compound leaf is said to be pinnate when the rachis or mid-rib bears a number of leaflets arranged in opposite or alternate manner. The rachis can branch off producing opposite or alternate manner. The rachis can branch off producing another rachis bearing leaves. The number of branching off from the main rachis determine further classification into unipinate, bipinnate, tripinnate and decompound. 
2. Unpinnate: This is when the rachis of pinnately compound leaf bears the leaflets directly. When the number of leaflets are even, it is said to be paripinnate whereas, if the leaflets are in odd number, it described as imparipinnate. E.g. of unipinnate are rose margosa. If the rachis of a pinnate leaf bears a single leaflet, it is called unifoliate, in pair (bifoliate), three leaflets (trifoliate), four leaflets (quadrifoliate) etc. 
3. Bipinnate: Remember these names are given according to the number of times the rachis branch off the main stem. While unipinnate of times the rachis branch off the main stem. While unipinnate is the first rachis that bears the first leaflets, in bipnnate, the first rachis produce secondary rachis which bears the leaflets. E.g. are sensitive plant and gum tree. 
4. Tripinnate: In tripinnate, the secondary axis give rise to a third or tertiary rachis that bears the leaves. E.g. drumstick. 
5. Decom pound: When the duplication of rachis goes beyond the tripinnate, it is described as decompound. E.G, carrot, coriander. 
6. Palmately Compound Leaf: Remember we had explained palmate venation to mean vein arrangement when the veins arise from the petiole and not from the mid-rib of the leaf. So palmately compound leaf shows a number of leaflets commonly joined like fingers arising from the petiole. 

E.g. silk cotton tree. Palmately compound leaves are classified according to the number of leaflet borne by a petiole. It is said to be unifoliate when there is a single leaflet, bifoliate (two leaflets), trifoliate (three leaflets), quadrifoliate (four leaflets), and multifoliate or digitate (five or more
leaflets).

GENERAL STRUCTURE, ANATOMY, PHYSIOLOGY OF THE ROOT

 Introduction

In unit 10, you studied the leaf of a flowering plant. In this unit you will study about the structure, anatomy, and physiology of the Root. You will study the main features of a flowering plant. a typical flowering plant is made up of the roots, the stem and the leaves, how the roots functions in taking up water is discussed. A lot of drawing has been included in this unit, learn how to draw the root, and how it takes water up.