Fasciation is caused by a change in the normal genes. As with proliferation the affected cells continue to mutiply and divide after they should have stopped. In this case they do so in a lateral manner so that instead of getting one stem or flower,you may get several that are fused together-sort of like Siamese twins. In most plants it is transient but in some plants the change is permanent and the affected part can be propagated as in the ‘cockscomb’ celosia.

Back view of 'Spray Cecile Brunner'showing fasciation of stem and flowers.

Front view of 'Spray Cecile Brunner' showing fasciation of flowers.