CHAPTER ONE
INTRODUCTION
1.1     Background of the Study
Growth is the irreversible increase in volume (size) number of part, length and weight of an organism (Umeh, 2004). Growth can be defined as a process by which a plant increase in the number and size of leaves and stems (Rayburn, 1993). Growth is also defined as an irreversible change in the size of a cell, organ or whole organism (Janick; 1979). Growth is an irreversible increase in body size and weight due to incorporation of new protoplasm in the body (sarojini et al; 1991). Growth is a physiological activity involving the enlargement and elongation of an organism  due to the incorporation of more protoplasm within the organism(Okeke; 2014). Cell theory states that new cells are formed from the pre-existing ones by division. When one   cell divides by mitosis, two new cells results. The two new cells put together are equal in volume or mass of the cells even though growth takes place in the number of cells. It is when the new cell grows to the maximum size of the parent cell that growth in volume is achieved. If those two new cells are arranged linearly, there will be an increase in length. The growth of both plant and animals require energy. Animal get their energy by digesting the plant they eat while plants get their energy from the sun through photosynthesis. Photosynthesis is the process where the green plant pigment in the plant leaf (chlorophyll) absorbs energy from sunlight and using the energy, water and carbon(iv)oxide to produce oxygen and simple sugar.
        The plant then uses these sugars to make more complex sugars and starches from storage as energy reserves, to make cellulose and hemicelluloses for cell wall or with nitrogen, to make protein. The way these plants uses energy depends on the developmental stage of the plants and environmental conditions.
        When leaves are removed from a grass or clover plant, new leaves develop and grow from buds on the crown or stems of the plants. This growth requires energy which comes from reserve carbohydrates (Sugar and starches) or from actively photosynthesizing leaves remaining on the plants. At some point, photosynthesis is great enough to produce more sugar than is needed for growth. This results in an increase in the reserve carbohydrate in the plant. As the leaf area increase further, leaves start shading one another and net growth shows as older leaves in shape do not get enough sunlight and begin to die. Root growth determines the ability of the plant to take up nutrient and water. Root growth determined by the plants activity photosynthesizing leaf area since the root depends on energy captured by leaves. Therefore roots receive energy only when more energy is produced by photosynthesis than is being used by top growth.
However, under drought conditions, the lack of water may reduce top growth while photosynthesis remains active. This results in accumulation of carbohydrate. The stems and roots have epical meristems responsible for extension growth which usually remains permanently embryonic and capable for growths for long periods (watering and Phillips 1970).
The effects of cool weather in the spring or fall are similar, cool temperature produces plant growth rate more than photosynthesis.
This calls for an increase in reserve carbohydrate in the plant and higher foliage quality. As plant matures, it increases in fibres and decrease in digestibility, crude protein and intake by livestock (Rayburn, 1993). In biology, everything that has life must grow and every living organism that grows must come to a peak or climax of the growth, death of old age will occur (Delvin, 1975).
        Sometimes, living organism such as plants and animals die before that maturity or old age due to certain circumstances that affects growth. Some of the factors that cause this premature death also affect the growth rate of plants and animals