In 1844, Ralph Waldo Emerson was looking forward to the great American poem. "We have yet had no genius in America... Our log-rolling, our stumps and their politics, our fisheries, our Negroes and Indians, our boats and our repudiations, the wrath of rogues and the pusillanimity of honest men, the northern trade, the southern planting, the western clearing, Oregon and Texas, are yet unsung. Yet America is a poem; its ample geography dazzles the mind, and it will not wait long for metres."
And it didn't have to wait long. In 1855, Emerson's hopes were answered with the publication of Leaves of Grass. Its author was, in his own words, "Walt Whitman, an American, one of the roughs, a kosmos..." And in Whitman's demotic, prophetic voice – Emerson called it a mixture of "the Bhagavad Gita and the New York Tribune" – the great American poem had suddenly arrived. But what about the great American painting?
That's the question posed by an exhibition at the Dulwich Picture Gallery. Coming of Age: American Art 1850s to 1950s, shows a collection of work borrowed from the Addison Gallery of American Art in Andover, Massachusetts (currently closed for a revamp). The show traces a trajectory – from provincial cringe to global triumph, stopping at the point, just after the Second World War, when Abstract Expressionism exploded and New York became the capital of the art world.
It's a rich display. There are about 70 works, hung densely on the walls, with almost every US artist you're likely to have heard of – Eakins, Homer, Sargent, Whistler, Bellows, Hopper, O'Keefe, Calder, Cornell, Reinhardt, Pollock – and including a handful of marvellous and surprising things.
But along with such names, you notice that each work is clearly labelled with its date. At every point, we are to know where we are in history's timeline. We can cross-refer to developments in European art. We can try to judge the decisive moments at which authentic American talent broke free from its past. When will the Whitman of painting arrive?
In the middle of the 19th century, Americans were expressing the same hopes for their visual art as for their poetry. America was a painting, too, after all, and in the year that Leaves of Grass appeared, the artist Asher B Durand issued this rallying cry – another list of artistic opportunities. "Our wild districts, the unshorn mountains surrounding them with their richly textured covering, the ocean prairies, and many other forms of Nature yet spared from the pollutions of civilisation, afford a guarantee of originality that you may elsewhere long seek and find not." (I quote from one of Dulwich's very well-chosen wall captions.)
True, Durand's roster of subjects is narrower than Emerson's. His ample geography includes no rogues, no stump politics, no Negroes or Indians, no trade, no plantations. It's landscape that he has in mind, pure landscape. America is virgin territory, unbroken ground, a land of unlimited uncultivated vistas – and that's where a truly American art will arise.
The first room in the exhibition has many early attempts at American landscape, including a glimpse of forest by Durand himself. These images are admittedly not the panoramic canvases that were shown in the American Sublime show at Tate Britain a few years ago. But even there, you saw how hard it was for the artists to find new forms for their new subject. They seemed to hope the subject by itself ("a guarantee of originality") would do it for them. But they couldn't shed European landscape habits: the framing devices, the well-mannered division into foreground, middle ground, background – all the tricks that civilise a view into a scene. In other words, they never learnt the lesson of Whitman.
He set himself deliberately to eliminate from his poetry all traces of the European literary heritage. He went over the drafts of Leaves of Grass again and again, removing the "stock touches". His roughness and free-speaking spontaneity are a fully conscious achievement. He laid down rules. "Make no quotations and no reference to any other writers." "A perfectly transparent, plate-glassy style, artless, with no ornaments." "Take no illustrations whatever from any ancients or classics." "Common idioms and phrases – Yankeeisms and vulgarisms..."
The tragedy of 19th-century American painting is that it never produced its Whitman. There was never a moment of absolutely abrupt originality. There was simply never an artist of his genius. But a Whitman of painting, some pictorial equivalent to his astonishing vision, in which democratic solidarity is expressed as sexual union, a merging of the poet's soul and body with the whole, wide world – well, can you even imagine what such a painting would look like?
There are glimpses. Thomas Eakins's candid, masculine eroticism, seen here in his picture of a taut-buttocked boxer, Salutat, holds a faint echo of Whitman's staggering sexual candour. (What other poet has addressed his own testicles so lovingly? "Sensitive, orbic, underlapped brothers"?) Or there's Winslow Homer's work, such as the briny seafarers of Eight Bells, with its close affinity to newspaper graphic illustration. That might be a visual match for Whitman's use of journalese, his "Yankeeisms and vulgarisms".
But the most Whitman-esque thing here is probably the work of that odd minor master John Frederick Peto. He specialised in trompe l'oeil images of doors and notice boards with bits and pieces stuck on to them. Office Board for Smith Brothers Coal Company shows an area of wooden-plank wall, with postcards, business cards, letters, leaflets, almanacs, bills, keys, bits of string – all the detritus of modern commercial life, randomly pinned on to it. There's a very good effect where a sticker has been torn off, leaving only its ripped corners.
Sure, Peto owes a lot to the 17th-century Dutch, who invented this kind of picture. But his miscellanies of stuff, casually laid out on a flat surface, are also the nearest that any picture of the time gets to a crucial aspect of Whitman's "democratic" aesthetic: his list-making, the potentially endless, additive, non-hierarchical lists, with which the poet reels off one vivid feature of the world after another.
These are only inklings. The openness and energy and daring of Whitman's "language experiment" (as he called it) are obviously lacking in Peto and in every other American painter of the 19th century.
But I pursue this "what if" or "if only" line of thought because Coming of Age is a show designed to put you on the alert for emerging signs of Americanness, and Whitman is clearly the boldest example of Americanness in the arts, and the one who sets a standard for all subsequent attempts.
He makes most 20th-century artists – however advanced – look pretty cautious and controlled. But his spirit does come through in a characteristic feeling of loose and relaxed improvisation. You find it in Stuart Davis's Red Cart, a very flat, fluid, cartoony accumulation of items on a wharf, or in Arthur Dove's Autumn, a pattern of unfolding blobs possibly indicating a landscape, or again in Milton Avery's Seagulls and John Marin's Movement: in both pictures, the sea becomes the occasion for a flotsam-and-jetsam form of painting.
Of course, this can't be the only standard. Tight control is the essence of Edward Hopper's art, the precise tuning of light and colour so as to bring the scene to poignancy. And Hopper's emphasis – the opposite of a great, embracing, democratic get-together – is on the (not necessarily unhappy) isolation of individuals, such as the man in Manhattan Bridge Loop, who walks along the street, unnoticed by the surrounding buildings and almost unnoticed by the painting itself.
But I think that, 100 years after, you do finally get something like a Whitman art, in Jackson Pollock's drip paintings. Look at Phosphorescence. The specifics of social reality are missing, and the mood is a bit too frantic, but the feeling of free, rough spontaneity, the expansiveness, the multitudinousness, the infinitude, the equality of every bit of the picture surface with every other bit, the merging of everything with everything, and of the artist's body with the work itself: that's the way ahead Walt pointed. Better late than never.
Coming of Age: American Art 1850s to 1950s, Dulwich Picture Gallery, London SE21 (020-8693 5254) to 8 June