HERE IS a mandala to celebrate the spring Japanese-style. A very large circular garden is girdled by a wall with tall pagoda gateways marking the points of the compass. Inside, a forest of cherry trees, laid out so that all may enjoy this annual spectacle, has erupted in great foaming pink and orange and white drifts of blossom. On a warm spring night, when the blossoms seem to float on the soft purple air, a vast domed frame has been erected over the trees, and strung with bunting and hung with colourful kites.