● The trees continue to `color{violet}"increase in height or girth"` over a period of time.

● However, `color{violet}"the leaves, flowers and fruits"` of the same tree not only have `color{violet}"limited dimensions"` but also `color{violet}"appear and fall periodically"` and some time repeatedly.

● All plant organs are made up of a `color{violet}"variety of tissues"`; so there any relationship between the `color{violet}"structure of a cell,"` `color{violet}"a tissue, an organ"` and the function they perform.

● All `color{Brown}"cells"` of a plant are `color{violet}"descendents of the zygote"`.

● The question is, then, `color{violet}"why and how"` do they have different `color{violet}"structural and functional"` attributes.

● `color{Brown}"Development"` is the sum of two processes: `color{violet}"growth and differentiation"`.

● To begin with, it is `color{violet}"essential and sufficient"` to know that the development of a `color{violet}"mature plant"` from a zygote (`color{violet}"fertilised egg"`) follow a `color{violet}"precise and highly ordered"` succession of events.

● During this process a `color{violet}"complex body organisation"` is formed that produces `color{violet}"roots, leaves, branches"`, `color{violet}"flowers, fruits, and seeds,"` and eventually they die.

● There are some of the `color{violet}"factors which govern"` and `color{violet}"control"` these developmental processes.

● These factors are both `color{violet}"intrinsic (internal)"` and `color{violet}"extrinsic (external)"` to the plant.

● `color{Brown}"Growth"` is regarded as one of the `color{violet}"most fundamental and conspicuous"` characteristics of a living being.

● Growth can be defined as an `color{violet}"irreversible permanent increase"` in size of an `color{violet}"organ or its parts"` or even of an individual cell.

● Generally, `color{violet}"growth is accompanied"` by metabolic processes (`color{violet}"both anabolic and catabolic"`), that occur at the `color{violet}"expense of energy"`.

● Therefore, for example, `color{violet}"expansion of a leaf"` is `color{violet}"growth."`

● `color{Brown}"Plant growth"` is unique because plants `color{violet}"retain the capacity"` for unlimited `color{violet}"growth throughout their life"`.

● This ability of the plants is due to the `color{violet}"presence of meristems"` at certain `color{violet}"locations in their body"`.

● The `color{violet}"cells of such meristems"` have the capacity to `color{violet}"divide and self-perpetuate"`.

● The product, however, soon `color{violet}"loses the capacity"` to `color{violet}"divide"` and such cells `color{violet}"make up the plant"` body.

● This `color{violet}"form of growth"` wherein `color{violet}"new cells"` are always being added to the plant body by the `color{violet}"activity of the meristem"` is called the `color{Brown}"open form of growth"`.

● The `color{violet}"root apical meristem"` and the `color{violet}"shoot apical meristem"` are responsible for the `color{violet}"primary growth"` of the plants and `color{violet}"principally contribute"` to the `color{violet}"elongation of the plants"` along their axis.

● In `color{violet}"dicotyledonous plants"` and `color{violet}"gymnosperms"`, the `color{violet}"lateral meristems"`, `color{violet}"vascular cambium"` and `color{violet}"cork-cambium"` appear later in life.

● These are the `color{violet}"meristems"` that cause the `color{violet}"increase in the girth"` of the organs in which they are `color{violet}"active"`.

● This is known as `color{Brown}"secondary growth"` of the `color{violet}"plant."`