The seed germinates to form a seedling which grows to form a young plant after some period, it bears flowers. The vegetative branches of a plant that do not bear flowers can be differentiated from the branch of a plant of the same species bearing flowers.
These branches which have not been born flowers yet are said to be in the juvenile phase and the branches with flowers represent the adult phase. The change may be shown by the gradual change in the shape of the lobes of the lamina. Examples are the leaves of the cotton plant or that of the Ipomoea.
In heteroblastic development, the change from juvenile to adult is abrupt so that the first few leaves are normal. In Acacia, the first leaves are normal and then suddenly they modify into phyllodes.
Heteroblastic development is also shown by Lathyrus aphaca when abruptly from the normal leaf formation, the tendrils are formed. It has been proved experimentally that the juvenile and the adult branches behave differently in physiological activities.
The juvenile branches when cut and propagated, bear roots quickly whereas the adult branches take a longer period. The cuttings taken from the adult branches of the Rose plant grow into small bushes.
Hormones breaking juvenility
The growth hormones also affect development. The adult branches treated with gibberellic acid, gibberellin result in the sudden growth of vegetative branches like in Ivy, …
Seedling of Eucalyptus when treated with gibberellic acid brings an early appearance of adult leaves as compared to untreated seedlings.