From peonies to chrysanthemums to dahlias, the reason why so many fireworks are named after flowering plants is because they burst out of a seed, or shell. Here are pictures of how it works.
1. Here is a 6 Inch cylindrical shell. The time delay fuse is at the far left ; square stars are in the left compartment; and the bursting charge extends through from the fuse to the black lift powder at right.
2. These star patterns are basically the prenatal image of a star shaped firework.
Each half of the shell will contain identical parts and when both halves are joined, the sides mirror each other.