CHAPTER-15
PLANT GROWTH AND DEVELOPMENT.

Growth is defined as an irreversible/ permanent increase in the weight and volume or size of an organism or its parts

 PRIMARY GROWTH.
 

¡When growth occurs due to the activity of primary meristems, (the meristems which arise from the beginning of plant life) and formation of primary tissues, it is called primary growth; it is growth in length.

¡Apical meristems are responsible for primary growth, mainly elongation or increase in length of plants along the long axis.

 SECONDARY GROWTH

 

¡When growth occurs due to the activity of primary lateral or secondary meristems, it is known as secondary growth; it is growth in thickness.

¡Lateral meristems like fascicular

 cambium and cork- cambium cause

 secondary growth and increase in

 the girth of the organs , where they

are functioning.

 PHASES OF GROWTH.

 

¡The meristematic region has cells that are rich in protoplasm, have a prominent nucleus, primary thin cellulosic cell wall with many plasmodesmatal connections.

¡The cell just above this region in the phase of elongation ; cell of this region show increased vacuolation, cell enlargement, deposition of new cell wall material etc.

¡The region just above the elongation zone is the portion where cells undergo maturation; the cell here attain their maximum size and protoplasmic modifications into various types.

 GROWTH RATE 

i.Measurement and comparison of total  growth per unit time -  called absolute growth rate.

ii.Growth of the given system per unit time and unit of the parameter – called relative growth rate.

 CONDITIONS FOR GROWTH.

 

¡Nutrients provide the raw materials for the synthesis of protoplasm and the energy needed for various metabolic functions related to growth. Water is necessary to maintain turgidity (extension growth) of cell and provides the medium for the functioning of enzymes for growth activities 
¡Oxygen is necessary for oxidation of the nutrients to release metabolic energy needed for the growth activities.
¡Temperature influences growth as every plants has an optimum range of temperature suited for its growth; any variation in temperature affects growth.
¡Light determine the direction of root and shoot growth; it is essential for photosynthesis and hence growth.
¡Growth also requires many mineral elements, whose deficiencies influence the rate of growth.