Question

Growth of leaf primordia is -
(a)First apical then marginal
(b)Only apical
(c)Only marginal
(d)Lateral

Answer 1

Hint: As we observe leaf growth in plants, they develop from the meristematic tissue of the shoot apex. Later in their growth, it is seen that they elongate and grow at specific intervals of the plant. Hence, their growth is not limited to one part of the plant.

Complete answer:
 Leaf primordia are groups of cells that will grow into leaves.
- The meristems responsible for the growth of the leaf are apical, adaxial, marginal, plate, and intercalary.
- Leaf development initiates in the apical meristem and gives rise to the leaf primordium. The leaf expands with cytokinesis in the apical and the marginal meristem.
- The continuous activity of these meristems leads to the lateral expansion of the lamina, with each half extending upward on either side.
- The leaf primordium grows upwards vertically and then expands laterally.

Additional Information:
 - Auxins and gibberellins are responsible for the formation of leaf primordia.
- Shoot apical meristem produces both leaf and flower primordia cells.
- The lateral meristem is that tissue that is arranged parallel to the parts of the plant and is involved in the increase of the girth of the plant. It is not involved in leaf formation.
- The continuous cell division leads to the leaf primordium curving upwards.

So, the correct answer is ‘first apical then marginal’.

Note: - The period between the initiation of two successive leaf primordia is known as Plastochron or Plastochrone.
- The development of the leaf primordium occurs in different locations on dicot and monocot plants. In dicots, it occurs in the second or third layer of the meristem while in monocots it may occur on the surface of the tunica.