he sat at the open partition that gave on to a handkerchief of garden and then the sea wall and gazed gloomily across the water at a giant statue of a man in a bowler hat and morning coat that tiger had told him was mr mikimoto , founder of the cultured pearl industry , who had been born at toba and had there , as a poor fisherman , invented the trick of inserting grains of sand under the mantle of a live oyster to form the kernel of a pearl .