Adnation    

Adnation is the union between floral parts of a different whorl or kind.

Examples

Union of Calyx & Corolla

Union of Androecium & Corolla

Datura Flower with Adnation between the Corolla and Androecium

Hypanthium = Fusion of Calyx, Corolla & Filaments without adnation to the Gynoecium produces a Perigynous Flower 

Perigynous Flower in the Rosaceae	Diagram of a Perigynous Flower

Union of Hypanthium to Ovary ->
Epigynous Flower with an   Inferior Ovary

Sectioned Apple (Pyrus) Flower This is an Epigynous flower!
Diagram of an Epigynous Flower similar to Fuchsia	Fuchsia an Epigynous Flower

Hypogenous flowers have their floral organs inserted below the gynoecium on the receptacle. This produces a "Superior Ovary"

Diagram of a Ranunculus Flower which is Hypogynous	Diagram of an Hypogynous Flower

Perigynous   -> Sepals, Petals & Stamens arise from the Hypanthium which surrounds the Ovary but is NOT fused to the Ovary Wall. The ovary is sometimes said to be "partly inferior" in cases like this.

Epigynous -> "Inferior Ovary" - Stamens, Petals & Sepals appear to grow from the top of the Inferior Ovary.