The Taoiseach may be in deep water over the spiralling costs and even the very concept of Sports Campus Ireland, but he deserves nothing but praise for initiating a process that led to the rescue from near ruin of the National Botanic Gardens in Glasnevin.

Of course, the gardens are located in his own constituency of Dublin Central, so the provision of funds for their renewal might be dismissed as mere clientilism. But it was because Bertie Ahern was familiar with "The Bots" that he was open to finding the money as Minister for Finance in the early 1990s.

Over the past 10 years, some £12 million (15.3m) -- a small fraction of the estimates for Abbotstown - has been invested in implementing a major development plan for the gardens. In the process, this important national institution has been released from what architect Ciaran O'Connor calls "an era of stagnation". Last week, the Taoiseach presented the RIAI's Silver Medal for Restoration to Mr O'Connor and his assistant, Michael Carroll, in recognition of their outstanding work on Richard Turner's great Curvilear Range - not least because it broke new ground in the use of innovative restoration techniques.

What distinguished the project was that all of Richard Turner's original ironwork that could be salvaged - amounting to some 87 per cent of the structure - was re-used in restoring the glasshouses; the remainder was metal from his glasshouse at Kew Gardens in London, which had been replaced by a cast aluminium replica.

Ten years ago, the Curvilinear Range was going to rack and ruin. Its restoration became a metaphor for the revival of the Botanic Gardens - once memorably described as "the brightest jewel" - and the fact that it wasn't a once-off but the first of a series of building projects boosted morale among staff in the gardens no end.

Donal Sinnott, director of the gardens, recalls that there was barely any time over the past nine years that the Office of Public Works didn't have builders on-site. And now, tenders are being sought to dismantle and restore the Great Palm House, whose jungle of plants was recently captured on camera by Amelia Stein.

One of Glasnevin's most urgent needs was a purpose-built library and herbarium. Priceless collections of books and dried botanical specimens had been stored all over the place, including dank basements, so it was important that they would be given a proper home, with the requisite internal environment to ensure their survival.

Ciaran O'Connor's red-brick building, with its curved windows overlooking the gardens, may have seemed somewhat incongruous in the context when it was completed. But its impact has been reduced by the new Visitor and Education Centre inside the main entrance, with which it shares a close architectural relationship.

The library and herbarium was shaped around a 150-year-old specimen Zelcova, an exotic tree known for its vase-like shape, which will probably last for another few hundred years. Chosen for its convenience to the Teagasc horticultural students, the site had been occupied by a fungus-infested grove of Sorbus. A curved brick wall forms the semi-circular entrance forecourt with a sculpture by Michael Quane representing elements of plant life in water, while Rois∅n de Buitleβr's frieze of botanical specimens in coloured glass is sandwiched between the double- glazing of an iroko screen at the entrance, bordered by a vertical strip of blue tiles.

Inside the extravagant foyer, which is used for occasional exhibitions, the botanical theme is continued with a series of low-relief plaster panels by Lisa Young showing important evolutionary plants. A well-lit curving staircase and gallery, from which the rare books collection is safely sealed, completes the architectural circle.

The first-floor reading room, with its Alvaar Alto furniture and solid beech shelving, enjoys an almost panoramic view of the gardens from a curiously curved set of windows, which Mr O'Connor insists are not "free-form" but rather segments of a circle; their built-in sun baffles are the same as those in the visitor centre.

Directly below, the herbarium is stored in compactors to the rear with its associated research library - not accessible to the public - laid out to allow specimens to be examined in natural light. The mainly blank exterior brick wall, facing north towards the Great Palm House, is to be planted with creepers to merge building and landscape.

A new suite of teaching rooms for the Teagasc students is housed, quite appropriately, in a timber-clad building with a sedum grass roof which they are responsible for maintaining. Located in one of the working ends of the gardens, it has a Scandinavian appearance, reflecting Mr O'Connor's architectural pre-occupations.

His Visitor and Education Centre replaces a random collection of pre-fabricated concrete boxes, a toilet block and security hut. A bird's eye view would show that its plan is inspired by the shape of a Horse Chestnut leaf, with its sharp point facing the entrance gates, and a clear demarcation between the public and more private areas.

The public face of the National Botanic Gardens is its set of gates, flanked by a pair of Edwardian houses festooned in Virginia creeper and twin lime trees right behind. This setting has been enhanced by re-paving the area in front with granite setts, though the cement-rendered wall alongside is still looking a little raw, even harsh.

A new car-park has been provided to the rear, opening up a second entrance to the gardens past an impressive 1940s glasshouse. Granite paving is used here too, with the intention of providing a patio for the cafeteria on the ground floor of the visitor centre; whether or not it will actually be used depends a lot on the weather.

The blank wall of the new lecture theatre is in brick - a variation of Flemish bond - to evoke a traditional walled garden and it has a very large, slightly recessed panel which is to be planted with creepers, just like the Library and Herbarium; this is typical of the thoughtful, considered response of the architects to their brief.

The bright, double-height foyer of the visitor centre, which can be entered from either end, is also paved in granite. Most of the doors are done in a geometric pattern of native and exotic veneers, as in the library and herbarium, to emphasise the use of natural materials and contribute to the graphic quality of the new building.

The foyer is dominated by a photographic print, nearly two storeys tall, of Glasnevin's giant Redwood. The stair - concealed behind a half-wall - is paved in polished slate and a recess at first-floor level contains more low-relief plaster panels of plants from the gardens collection, which amounts to 20,000-plus specimens.

A continuous run of windows with deep-shelf sun baffles flood both the cafeteria and more formal upstairs restaurant with natural light. The elevated view from the restaurant, with its maple tables and Mies chairs, is panoramic; a single angular projection lines up precisely with the central house of Turner's Curvilinear Range.

Fretted acoustic panels underneath the windows mitigate noise from the oak floor. Acoustics in the 150-seat lecture theatre are also superb, due to the use of a stepped ceiling and a fretted timber wall at the rear. Its stage area is backed by beech veneer panels though, unfortunately, the sliding doors over the screen are done in oak.

With gardening so popular these days, the theatre should be used much more often for public lectures as part of a concentrated outreach programme; even as an acknowledgement of the Exchequer and EU funding for the renewal of the Botanic Gardens, that would be one way of giving something back to the public.