Sowing the seeds.

Using bentwood in building is an ancient practice, traditionally common, for example, in the constructions of such disparate cultures as Mongolian yurts and Zulu round houses. The delight of these organic looking confections consists in appreciation of the geometric precision underpinning peculiar tradition, craft and apparent spontaneity. Conversely, the latter qualities seem to exist in modern, more self-conscious elaborations of the basic type.

Hooke Park school and research centre in Dorset, locally built of local green forest thinnings, was designed' with contemporary engineering vision, but the first impression on seeing the building crouching in a clearing is of something much more ancient. Materially rustic, but simple in outline and complex in underlying constructional principles, its appeal, like that of the weaver bird's nest, is atavistic.

The idea of engineered rusticity, drawing on local supplies of wood to create an economic structure appropriate to purpose and climate, lends itself naturally to the cause of green architecture - the proviso of course being ecological harvesting of the basic material.

In Belgium, Samyn et Associes' design of a new seed house and forestry centre, at Marche-en-Famenne, follows Hooke Park in drawing on local resources and engineering expression, but takes the type a step further away from craft, looking back to Paxton and ahead to the poetry of modern engineering. But still, aesthetically, there is the same intriguing tension. The plan of the building is a pure ovoid, appropriately so considering its seminal purpose; but its scale and toroidal(2) carapace make it endearingly biomorphic.

The seed house is set in a grove of 200 year old oak trees and is devoted to sylviculture, providing facilities for testing, nurturing and storing seeds from the Walloon forests. Its presence is a result of the federalisation of Belgium, and the Walloon Region's public commitment to independence, to local ecology and to economic prosperity. In providing forest thinnings for the seed house's construction, the Walloon administration asked for a structure showing What adventurous things could be done with wood. The domed cover of the building is a toroidal framework of bentwood arches, each clamped at the bottom to a reinforced concrete apron; each is double layered, curved and composed of pieces of wood of rectangular section. Arches run cross-wise and lengthwise to ensure threedimensional stiffness. The frame is covered with large tiles of laminated reflecting glass. Within the dome are subsidiary structures - concrete boxes from which struts spring to take some of the horizontal loads. The boxes contain laboratories, storage and off ices. The central nave is reserved for large machines that treat and dry seeds.

After extensive tests, Samyn abandoned the idea of using a development of the Hooke technique of bent green wood. Tests had suggested the wood would crack on being subjected to rapid drying as it would be in this case. The industrially dried wood for the seed house was bent by steam moulding, and then impregnated with fungicide and insecticide before being dried out.

The wooden structure with its raincoat-like covering provides little protection against the cold. In winter, radiant panels in the work zones ensure a comfortable ambient temperature and a ventilation system removes excess humidity and reduces condensation - particularly important when pine cones and other humid seeds have been gathered in. In summer, the building's envelope of laminated reflective glass reduces insolation; the frame and the overhanging trees shade the building. Fresh air can be admitted through vents along the bottom of the dome, with stale air being drawn up through ducts and expelled over the west door.

The sense of scale and order in this enchanting - and essentially modest - building reaches exhilarating heights internally. The light-striped nave with its soaring arches encloses the functions of the building in a contemplative and ecclesiastical atmosphere.

(1) By Ahrends, Burton & Koralek, with Buro Happold and Frei Otto (AR May 1990). (2) A toroid is formed by rotation of a point round a constant curve. If this curve is a circle, the resultant form is a ring or torus, The form here is a segment of a torus cut by a plane parallel to a diameter