Roots are feebly developed in

The root apex is subterminal because it

The lateral roots generally originate in

The smallest region of the root is:

Roots obtain oxygen from air in the soil for respiration. In the absence or deficiency of $O_{2}$,root growth is restricted or completely stopped. How do the plants growing in marsh lands or swamps obtain their $O_{2}$ required for respiration?

The cells of this region of the root are the smallest.