With the Autumn Equinox approaching, many groups enact what is know today of the ancient Greek rites, the "Eleusinian Mysteries", and in particular the mourning of the Grain Goddess, Demeter.
According to myth, Demeter taught mankind the art of sowing and ploughing so they could end their nomadic existence. in turn, what was harvested was used in offerings to the Gods.
When her daughter, Kore (meaning "maiden") was abducted by the God of the Underworld, Hades, Demeter went into mourning, and wandered the world in search of her child. A result of her neglecting her duties was that crops failed to grow, which meant the people started to starve. The shortage of food also meant that the Gods didn't get their offerings.
Eventually Zeus (the leader of the Olympian Gods) stepped in and the messager of the Gods, Hermes, was sent into the Underworld with an order to Hades to return Demeter's daughter. During her time in the Underworld, Kore had eaten a few seeds from a pomegranate (a common fertilty symbol) thus she was no longer a "maiden". Instead, she was transformed in Persephone.
The eating of these few seeds bound Persephine to the Underworld for a third of the year. And it is only when her daughter is with her, Demeter lets things grow (summer). The dying and blossoming of nature was thus connected with Demeter.