Complex sentence: His father was the Rector of Lamorran, a keen gardener of one of the finest gardens in Cornwall, and his uncle was Evelyn Boscawen, 6th Viscount Falmouth who was developing a garden on his estate at Tregothnan.
Split into simpler sentences: His father was the Rector of Lamorran, a keen gardener of (it was said) one of the finest gardens in Cornwall. His uncle was Evelyn Boscawen, 6th Viscount Falmouth who was developing the garden on his estate at Tregothnan.