Describing a Flowering Plant

Introduction

It is impossible not to be fascinated by the variety of structures found in higher plants. A large diversity of angiosperm morphology can be found in external structures, but they all possess roots, stems, leaves, flowers and fruits. The root system is underground in flowering plants, while the shoot system is above ground. The flowering plant can easily perform the process of fertilisation.

The root-

 Root is non green, cylindrical and descending part.Positively geotropic.

     Parts of roots:

1.Root cap zone – The root is covered at the apex by a thimble-like structure called the root cap . It protects the tender apex of the root as it makes its way through the soil                                           

2.Zone of cell division- A few millimetres above the root cap is the region of meristematic activity. The cells of this region are very small,thin-walled and with dense protoplasm. They

divide repeatedly. 

3.Zone of cell elongation-    The cells proximal to this region undergo rapid elongation and enlargement and are responsible for the growth of the root in length. This region is called the  region of elongation.

    4.Zone of maturation or Root hair zone- The cells of the elongation zone gradually differentiate and mature. Hence, this zone, proximal to the region of elongation, is called the region of maturation. From this region some of the epidermal cells form very fine and delicate, thread-like structures called root hairs. These root hairs absorb water and minerals from the soil.

Types of Roots-

• Tap Root – Development directly from radicles and usually present in dicots. The primary root continuously grows. They always develop below the soil. The single main root gives rise to the fine lateral roots                                                               
• Adventitious Root – Development from any plant part except radicle and usually present in monocots.The primary root stops to grow.They may be underground or aerial in the ground. They form a cluster of roots which may arise from the same point.

 The stem

Are there any characteristics that distinguish a stem from a root? An axis’ stem is the ascending portion that bears its branches, leaves, flowers and fruit. The plumule of a germination seed develops into this organ. Each node and internode are located at the same point along the stem. Nodes are those parts of the stem where leaves form, while internodes are the parts of the stem between nodes.

The leaf

Leaflets are generally flattened, lateral structures that hang from the stem. A bud develops in the axil at the node of the stem; this developing axillary bud becomes the branch of the plant. An acropetal arrangement characterises the leaves that arise from shoot apical meristematic. Leaves are the most functional vegetative organs for photosynthesis.

The inflorescence

Flowers are modified shoots created by converting the shoot’s apical meristem into a floral meristem. It does not elongate and condenses on the axis. In front of successive nodes of the plant, the apex produces different kinds of floral appendages instead of leaves. The start of a shoot always becomes a solitary flower. Florescences describe flower arrangements along the floral axis.

The flower

The function of flowers is reproduction. Angiosperms reproduce their seeds in their flowers. Flower heads are typically composed of up to four types of whorls arranged sequentially at the swelling end of the stalk, called the thalamus or receptacle. The following forms are present: calyx, corolla, androecium and gynoecium. Androecium and gynoecium are reproductive organs, whereas calyces and corollas are accessory organs. Several flowers, like the lily, do not separate the calyx from the corolla, and these are called perianths. The androecium and gynoecium are both present in a bisexual flower. In a unisexual flower, either a stamen or a carpel is present.

The parts of a flower

In general, each flower has four floral whorls, namely the calyx, the corolla, the androecium and the gynoecium.

Calyx

The collective term for the outermost whorl of a flower is calyx. It comprises green, leaf-like structures called sepals and protects the bud. Polysepalous(free all sepall) calyx are those with separate sepals, while gamosepalous (fused all sepal) calyx are those with fused sepals.

Corolla

The next whorl of the flower is the corolla. It comprises brightly-coloured petals to attract pollinators. Petals are either gamopetalous (all petals fused) or polypetalous (all petals free). The shape and colour of the corollas are significantly different in different plants; they can be tube-shaped, bell-shaped, funnel-shaped or wheel-shaped. 

Aestivation is the way the sepals and petals are arranged in relation to each other in a flower bud. Valvate, twisted, imbricate and vexillary aestivation are the most common arrangements.

Sepals or petals in a whorl are valvate if they just touch each other at the margins, as in Calotropis. 

In a twisted arrangement, the margins overlap, as seen in China roses, lady’s fingers and cotton.

As in Cassia and Gulmohur, imbrication occurs when the margins of petals and sepals do not overlap in any precise direction.

In vexillary or papilionaceous aestivation, the largest petal (standard) overlaps the two lateral petals (wings) on either side, and these overlap the two smallest anterior petals (keels). Pea and bean flowers display this type of aestivation.

 Androecium

The androecium consists of pistils and stamens. The male reproductive organ, stamen, is composed of a stalk or filament and an anther. Typically, anther lobes have two chambers or pollen sacs; anthers are bilateral. During pollination, pollen grains form in pollen sacs. The staminode, which is the sterile part, is formed during this process.

An individual stamen may join another stamen or petal. Stamens attaching to petals are epipetalous, as they do in  epiphyllous if they attach to the perianth, as they do in lily flowers. An individual stamen may stay free in a flower (polyandrous) or may be fused.  

In China rose, the stamens are united into one group (monadelphous), whereas in a pea they are divided into two groups (diadelphous). Citrus has more than two groups (polyadelphous). Depending on the species, filaments may vary in length within a flower, for instance, Salvia and mustard.

Describe the life cycle of a plant

As part of its life cycle, a flowering plant undergoes the following events:

• Gametogenesis:Formation of special haploid cells, the gametes, by meiosis  
• Pollination: Wind or insects carry pollen from one flower to another. This process is called pollination.
• Fertilisation: The pollen fuses with the gametes in the ovary of the flower, where they develop into males. Fertilisation occurs at this point.
• Dispersal: As seeds fall to the ground, they are scattered by the wind and by animals. These seeds can sprout into new plants.
• Germination of seed:This occurs when seeds are planted and begin to grow. Roots form below the soil, while leaves and stems appear above the soil.

Thus, we can see that a plant’s life cycle begins with a seed. When the seed germinates, it turns into a seedling. As the seedling develops, it becomes a new plant that produces new seeds, thereby continuing the cycle.

Conclusion

There are two types of reproduction in plants, referred to as generations. The generations move in and out of existence in a circular motion. Hence, every plant has two successive generations that alternate during its life cycle. These successive generations are referred to as alternations of generations.