When an atom splits into two parts it releases energy. this is called fission and vegetative propagation is  defined as if one plant is involved and the offspring is the result of one parent. The new plant is genetically identical to the parent.this is called vegetative is a form of asexual reproduction .

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in biology , fission is the process by which one cell gets divided in to two parts or more.
vegetative propagation is a type of asexual this type of reproduction only one plant is involved and the new plant grows on the parent plant.