Sub- aerial Modifications : Stem of some plants remains sub- aerial which grow horizontally on the surface of the soil for the purpose of reproduction.
There are four types.
1. Runner: The stem grows laterally on the surface of the soil, breaks up to produce roots where it touches the ground to give rise to new plants.
Eg: Centelk (Vallarai).
2. Stolon: Stolon is a slender branch of the stem that grows upwards to some distance and then bends towards the ground. Upon touching the ground, it gives rise to a new plant.
Eg. Wild strawberry.
3. Sucker Sucker is a short and weak lateral branch that grows diagonally upwards and directly gives rise to a new shoot.
Eg. Chrysanthemum.
4. Offset: An offset is a short and thick branch that arises from the axial part of a leaf. It has thick intemodes. It produces a tuft of leaves and cluster of small roots below.
Eg: Eichhornia.
