The correct option is A Both assertion and reason are true and reason is the correct explanation of assertion.
Growth can be defined as a permanent or irreversible increase in dry weight, size, mass or volume of a cell, organ or organism.
Growth in plants is exceptional because some of them retain the ability of unlimited growth throughout their lifetime. In plants, growth is accomplished by cell division, increase in cell number and cell enlargement.
In lower plants, growth is diffused as every cell can divide and enlarge. Higher plants possess specific areas in their apical portions, specially in the root apex and shoot apex, which take part in the formation of new cells. These are called meristems. This form of growth where there is addition of new cells to the plant body by the activity of meristematic cells is called open form of growth.
Growth in plants is localised owing to the fact that growth happens only at regions of meristematic cells.