Question

why to cotyldons fall of when plant grow​

Answer 1

Answer:

This is generally just a few days and then the seed leaves fall off. They remain to help direct the energy stored in the seed to new growth, but once the plant is self-sufficient, they are no longer needed.

Answer 2

Answer:

Because it is a storage organ, the cotyledon is an inefficient provider for the adult plant, so it will shrivel and fall away from the plant as shade from the growing plant covers it, either because of senescence or because it is being edged out by an emerging root.