There is a large diversity in external structure or morphology of plants; they are all characterized by presence of roots, stems, leaves, flowers and fruits. Figure 16.1 shows the parts of a flowering plant.
In most of the plants, the direct elongation of the radical leads to the formation of primary root which grows inside the soil. It has lateral roots of several orders that are known as to as secondary, tertiary, etc. Refer Fig. 16.2. Covers is covered at the apex by A thimble-like structure it is known as the root cap as shown in Fig. 16.3. The tender apex of the root as it makes its way through the soil, therefore, it is protected.
Roots in some plants change their shape and structure and become modified to perform functions other than absorption and conduction of water and minerals as shown in Fig. 16.4. They roots are modified for support storage of food and respiration as shown in Fig. 16.5.
Root is the water- and mineral-absorbing part of a plant which is usually underground, does not bear leaves, tends to grow downwards and is typically derived from the radical of the embryo.
Step develops from the plumule of the embryo of a germinating seed and it is the stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. The stem has nodes and internodes. The stem regions where leaves are come out are called nodes while internodes are the portions between two nodes.
The stem bears buds. These may be terminal or auxiliary. Stem is generally green initially and later often become woody and dark brown. The stem spreads out branches bearing leaves, flowers and fruits. It conducts water, minerals and photosynthesis. Some stems store food, support, protection and of vegetative propagation. Stems are modified to perform different functions as shown in Fig. 16.6.
The main stem or a branch of the main axial system of a plant, developed from the plumule of the embryo and typically bearing leaves. A slender or elongated structure that supports a plant or fungus or a plant part or plant organ. Parts of the plant shoot above ground level that gives rise to the presence of leaves which are equally separated by nodes.
The leaf is a lateral and normally flattened structure borne on the stem. Leaf develops at the node and bears a bud in its axil. The auxiliary bud later becomes into a branch. Leaves originate from shoot apical meristems. They are arranged in an acropetal order and are the very important vegetative organs for photosynthesis.
A leaf has three main parts namely leaf base, petiole and lamina as shown in Fig. 16.7. The leaf is attached to the stem by the leaf base and may bear two lateral small leaf like structures called stipules. The leaf base expands into a sheath covering the stem partially or wholly in monocotyledons.
When leaf lamina is entire or when incised a leaf is said to be simple. The incisions do not touch the midrib. When the incisions of the lamina reach up to the midrib breaking it into a number of leaflets, the leaf is known as compound. A bud is present. Both simple and compound leaves have a bud in the axil of petiole, but not in the axil of leaflets of the compound leaf does not have bud.
Figure 16.8 shows the compound leaves which may be of two types. In a innately compound leaf a number of leaflets are present on a common axis, the rachis, which represents the midrib of the leaf similar to presence in neem.
The leaflets are attached at a common point in palmately compound leaves. That is the tip of petiole as in silk cotton. The pattern of arrangement of leaves on the stem or branch. This is usually of three types namely alternate, opposite and whorled as shown in Fig. 16.8. Leaves get often modified for climbing as in peas.
Leaf is a special organ of vegetation in the form of a lateral outgrowth from the stem, whether appearing as a part of the foliage, or as a cotyledon, a scale, a bract, a spine, or a tendril.
A flower is basically a modified shoot wherein the shoot apical meristem changes to floral meristem. Internode does not elongate and the axis gets condensed. The apex gives different kinds of floral appendages laterally at successive nodes instead of leaves. It is always solitary when a shoot tip transforms into a flower. The arrangement of flowers on the floral axis is known as inflorescence. Two major types of inflorescences get defined as racemes and cymosely depending on whether the apex gets converted into a flower or continues to grow.
The main axis continues to grow in recompose type of inflorescences. The flowers are borne laterally in an acropetal succession as shown in figure in cymosely type of inflorescence; the main axis terminates in a flower which is limited in growth. The flowers are borne in a basipetal order.
Inflorescence is the group or arrangement in which flowers are borne on a plant.
The reproductive unit in the angiosperms is the flower. It is for sexual reproduction. A flower has four different kinds of whorls arranged after another the swollen end of the stalk or pedicel. This is known as thalamus or receptacle.
These are calyx, corolla, androecium and gynoecium. Calyx and alia are essential organs. But androecium and gynoecium are reproductive organs. A flower having both androecium and gynoecium, is bisexual. A flower with either only stamens or only carpels is unisexual.
The flowers are described as hypogynous perigynous and epigenous the position of calyx, corolla and androecium in respect of the ovary on thalamus. Each flower generally has four floral whorls, namely. Calyx, corolla, androecium and gynoecium.
Flower is the sexual reproductive structure of the angiosperms, typically consisting of gynoecium, androecium and perianth and the main stem bearing these parts.
The fruit is an outcome of the flowering plants. It is basically a mature or ripened ovary, developed after fertilization. If a fruit is formed without fertilization of the ovary, it is known as a parthenocarpic fruit. Normally, the fruit consists of a wall or pericarp and seeds. The pericarp may be dry or fleshy. Pericarp is differentiated into the outer epicarp, the middle mesocarp and the inner endocarp has is thick and fleshy.
The parts of fruit are shown as Fig. 16.13. Mango and Coconut develop from monocarpellary superior ovaries and are one seeded. In mango the pericarp is well differentiated into an outer thin epicarp, a middle fleshy edible mesocarp and an inner stony hard endocarp in mango. The mesocarp is fibrous in coconut.
Fruit is the seed-bearing structure in angiosperms formed from the ovary after flowering.
After fertilization the ovules, develop into seeds. A seed consists of a seed coat and an embryo. The embryo consists of a radical, an embryonal axis and one or two cotyledons. The outermost covering of a seed is the seed coat.
The seed coat has two layers, the outer testa and the inner tegmen. Within the seed coat is the embryo, consisting of an embryonal axis and two cotyledons. The cotyledons are often fleshy and full of reserve food materials. In plants such as bean, gram and pea, the endosperm is not present in mature seeds.
Normally, monocotyledonous seeds are endospermic but some as in orchids are non-endospermic. In see Fig. 16.15. The endosperm is bulky and stores food. The outer covering of endosperm separates the embryo by a portentous layer called aleuronic layer. The embryo is small and situated in a groove at one end of the endosperm. It consists of one large and shield shaped cotyledon.
Shape, size, structure, mode of nutrition, life span, habit and habitat vary flowering plants. They have well developed root and shoot systems. Root system is either tap root or fibrous. Generally, dicotyledonous plants have tap roots as shown in Fig. 16.15. Monocotyledonous plants have fibrous roots.
The roots in some plants get modified to serve as storage of food, mechanical support and respiration. The shoot system is differentiated into stem, leaves, flowers and fruits. The morphological features of stems help to differentiate the stems from roots.
Seed is a propagating organ formed in the sexual reproductive cycle of gymnosperms and angiosperms, consisting of a protective coat enclosing an embryo and food reserves.