When I showed a friend one of Rodney Graham's inverted oaks, he said it made him feel that this is how trees are supposed to be seen. That this is, as it were, the "right" way up. And there is, it's true, a peculiar rightness about these images, a series of monochrome photographs of huge, solitary Quercus robur that have simply been mounted upside down on the gallery wall. Their boughs no longer struggle upwards but billow effortlessly down into gaping sky-chasms, seem to hang like bats from earthy ceilings. Masters of a logically absurd world in which we'd helplessly plummet, their hidden roots have become both crown and saviour. Of course, the reason for the odd familiarity of Graham's Oxfordshire Oaks (1990) could be that this is how images enter our heads. Passing through the pinhole of the eye, light from the external world creates an inverted image that the brain subsequently "corrects". But it's with that vertiginous scene, that terrifying world in which sky and earth have switched places, that reality first declares itself to us.
Graham's interest in inversions comes from his obsession with the camera obscura, itself in effect a crude, room-sized, enterable eye. Clamber into Camera Obscura Mobile (1996), one that he's made by converting a 19th-century mail carriage, and you can see where he's coming from. As the groan and squeak of the old suspension fades away, you notice a delicate mass of gravity-defying fronds on a screen on the opposite wall. If the pictured palm seemed merely tacky in its pot on the gallery floor, nothing but a glorified house plant, its luminous image in this cramped, darkened chamber is, well, something special. As the artist has written, it can sometimes be necessary "to turn one's back on the thing one hopes to see". The Oxfordshire Oaks series attempts to do away with the need for bulky apparatus by simply up-ending photographs, but I wonder whether something vital hasn't been lost in the process. A tree whose roots are branches and whose soil is light and air is an unforgettable image, a startlingly clear symbol of life after death, but the illumination in the carriage has something else besides. It shines in darkness, like a painting in a cave.
The cave painting viewed by the light of a flaming torch is evoked even more surely by another, much earlier work: 75 Polaroids (1976) is the culmination of an experiment which involved Graham crashing blindly through woods and parks in the dead of night, snapping away with his Polaroid camera. A selection of the resultant images is displayed in a dark room, shots of startled-looking branches and trunks that the flash has given the russet warmth of the Altamira bison. Lit for a split second, conifer and fern appear as if caught in the midst of some secret, surreptitious rite. Once again, the theme is illumination. Just as prehistoric man descended into murky depths to see the magnificence of his prey, and just as Graham has used the camera obscura to view the delicate beauty of trees, so this little cave gives us glimpses of the Arcadia that familiarity obscures. The darkness of the woods is thus a metaphorical as well as a literal one, standing for the spiritual darkness that the artist tries to lift by his brief, fumbling interventions.
Having established illumination as Graham's fundamental concern, it becomes easier to make sense of an initially baffling exhibition, to sort the key works from the minor variations. It helps you view a piece such as Aberdeen (2000), a slide-show recording a pilgrimage to the "redneck town" famous for being the birthplace of Kurt Cobain. Graham mentions in his notes that "the grey weather gave way to beautiful sunshine" for the duration of his short visit - and, sure enough, the slides reveal a shabby nowheresville transfigured by beneficent winter light. Fortuitous perhaps, but can it also be coincidence that the whole trip puns on the idea of searching for Nirvana? Graham's preoccupation with "loops" can also be understood in terms of the conflict between drudgery and beauty, darkness and light. The Romantic novel short-circuited so that the protagonist never escapes the forest, those films whose characters are locked into an endless cycle of humiliations - what are these but images of souls that have lost their vision and their way? Similarly, Halcyon Sleep (1994) shows the artist slumbering on the back seat of a car, oblivious to the glitter of the city he's being driven through. In all his work, then, Graham seems to be acknowledging two possibilities - the one of illumination, and the other, perhaps inevitable, of sleepwalking through eternity.
"Rodney Graham" is at the Whitechapel Art Gallery, London E1 (020 7522 7888), until 17 November
