Question

parts like petals androecium wither and fall down after fertilization.The pedicel,thalamus and calyx become stronger.explain reason

Answer 1

After fertilization, corolla and androecium are withered away, also stigma and style of gynoecium withered away. In some species calyx persists. Whereas pedicel become stronger to hold the fruit. Thalamus or receptacle of a flower is a platform on which ovary develops into fruit. To bear the weight of fruit these becomes stronger.  

Answer 2

Answer:

A normal flower can be divided into four parts and they are the calyx or sepals, corolla or petals, Androecium defining the male reproductive organ and Gynoecium the female production organ.

The calyx withers after fertilization.

The ovary turns to the fruit and the seed as ovum after fertilization so they are hard.