Pea

Scientific name: Pisum sativum.

Pea is a common and well-known crop plant. It produces flowers, fruits and seeds. So it is a flowering plant, it is an annual, herbaceous climber.

Parts of pea plant:

A pea plant has two main parts: root and shoot. The root grows within the soil while the shoot is the above ground portion of the plant.

Root system:

The root system always develops from the embryonic root (radical) of a seed. The persistent main root that grows from radical is known as tap root or primary root, which grows deep into the soil. The lateral; branches developing from the primary roots are known as secondary roots. These roots again branch out finer roots which are known as tertiary roots. The tap roots and its branches and sub-branches together constitute the tap root system.

The roots penetrate deeper and deeper into the soil. So there is every possibility of friction between the tip of the root and the soil particles. Hence, the soft, delicate tip of the root is protected by a cap-like structure called root cap. Behind the root cap region there is a very short region called the region of growth, because the root increases in length due to rapid expansion of this region. Just behind this region, the root bears numerous hair-like unicellular structures called root hairs. The region bearing the root hairs is known as root hair zone. These root hairs play an important role in plant’s life. They help the plant in absorbing water and nutrients from the soil. Beyond the root hair region, the region of the root extending up to the base of the stem is known as the permanent region. Secondary roots usually arise from this region.

The overall function of roots is to absorb water and nutrients (minerals) from the soil and pass it to the stem. It also helps the plant in fixing firmly with the soil. But in pea plant’s life, an additional important function is noticed. In the roots of pea plants there are many swollen structures known as nodules. In these structures a kind of bacteria called rhizobium grows. These bacteria have the ability to fix (transform) atmospheric nitrogen compounds. The pea plant gives shelter and supplies food to these bacteria and in exchange these bacteria give the pea plant nitrogen to meet its nitrogen demand. In the way, the two organisms live with mutual co-operation. This type of living is known as symbiosis and the individuals are known as symbionts.

Shoot system:

The part of the plant which grows above ground is called the shoot. The shoot system consists of:

1. Stem: The stem of pea is generally very soft, weak and greenish is color. They attain various heights. There are some relatively swollen, harder points in the stem from where leaves branches arise. These points are known as nodes. The space between two nodes is known as inter-node. The angle is formed between the stem and the leaf is called axils. Buds found at the tip of the main stem are known as terminal buds, while those arising at the axils are called axillary buds or lateral buds. Each axillary bud may give rise to a branch or a flower. The stem produces and supports branches, leaves, flowers and fruits. It also helps in the conduction of water and minerals from root to the leaf and prepared food from the leaf to different parts of the plant.

2. Leaf: The flat green and lateral outgrowth arising at the node of the stem or its branches is called a leaf. In pea plant, the leaves are compound. By compound leave s it is meant that each leaf is composed of several small leaflets. In pea, 3 to 4 pair of leaflets is arranged on two sides of a central axis. The terminal leaflets and some of the upper lateral ones are modified into coiled thread-like structures called tendrils. It helps the plant is climbing a support. In pea plant, at the base of the leaf two broad leaf-like outgrowths encircling the node are present. These are called foliaceous stipules. The pea leaf has a long stalk (petiole). There are many fine lines on the leaf blade (lamina), known as veins. The arrangement of veins is known as venation. Through the veins conduction of water, minerals and organic food takes place. The leaf contains chlorophyll (green pigment) and helps the plants in manufacturing food, taking part in gaseous exchange (respiration) and giving of excess water through the process known as transpiration.

3. Flower: In pea, three to four flowers appear in a cluster which is known as inflorescence. Flower is usually white or light pink in color and looks like a butterfly. It has a small stalk and it consists of four whorls (parts) viz.

• Calyx: Calyx is the lowermost green tubular part of the flower. It consists of five slightly unequal lobes called sepals. It protects the other whorls in the bud stage from possible external injuries.
• Corolla: It consist of five petals of different shapes and sizes. The outermost petal is the largest and spreading and is known as standard or vexillum which covers the other petals in the bud stage. The next two lateral petals look like wings. Hence they are called wings or alae. The two innermost ones unit loosely along their ventral margins to form a boat-like structure and are known as keel or carina. The attractive color and sweet scent of the corolla attract insects for pollination.
• Androecium: The third whorl of pea flower is called androecium or male whorl. It consists of ten stamens, of which nine are arranged in a bundle and one is free. A stamen has two parts – filament and anther. The filament is a long stalk which is capped by a sac-like structure called anther. The anther carries pollen grains within it.
• Gynoecium: The fourth whorl is gynoecium or female whorl, which is located at the centre of the flower. It consists of three parts viz. ovary, style and stigma. The flattened, broad basal portion is known as ovary which continues into a short stalk known as style. The style ends into a sticky, feathery body called stigma. The ovary is transformed into a fruit.

4. Fruit: The fruit of pea is called pod or legume. It is green in color. Within the fruit, the seeds are arranged in a row. After maturity burst and distribute the seeds. The seeds are globular and covered with a thin seed coat. Each seed consists of two round parts called cotyledons. Hence, the seeds are known as dicotyledonous seeds and such plants producing dicotyledonous seeds are known as dicotyledonous plant. The seeds on germination give rise to news pea plants.