This book is about different ways of looking at flowers - artistically rather than scientifically, but not simply as decoration. The chosen examples represent the art movements of their time, together with something more extreme and passionate coming from the individual artists. Georgia O''Keeffe wrote: ''Nobody sees a flower - really - it is so small - we haven''t time - and to see takes time like to have a friend takes time. So I said to myself I''ll paint what I see, what the flower is to me, but I''ll paint it big and they will be surprised into taking time to look at it.'' O''Keeffe was fascinated by arums (like Diego Rivera who repeatedly painted waxy-white calla lilies). She painted a series of six entitled Jack-in-the-pulpit, each growing increasingly abstract as she zoomed into the centre of the flower. Such dramatic close-ups were also well suited to another sexy flower, the orchid, which is adapted more flamboyantly than most species to waylay pollinating insects, for which purpose it sports protuberances and patterns that also intrigue humans. O''Keeffe chose Brassavola hybrids, and Gary Hume painted slipper orchids, but the trend had begun earlier with the travels of Marianne North, a Victorian lady painter, who set her dramatically enlarged comet orchids among tropical vegetation and butterflies; and with Martin Johnson Heade who journeyed to Central America for inspiration and painted cattleyas looming from jungle landscapes amid humming birds.

They also painted roses; almost everyone from Botticelli to Cy Twombly has painted roses. This book could easily have been of roses alone and through them the history of both art and horticulture could have been traced. For two centuries before flowers actually became the subject of artworks white roses appeared in religious contexts alongside the Virgin Mary to represent her purity and spirituality, while red roses symbolised the redeeming blood of Christ. These were the two traditional roses of Europe, semi-double with their golden stamens glowing in the centre of the flower. Then, early in the seventeenth century, the Spanish artist Zurbaran painted a mystic still life of vessels associated with the Mass, with one damask rose, a species which is white but blushes pink as it opens. This rose may symbolise the Virgin conceiving Christ, or the water in the cup about to be miraculously turned to wine. For rose historians it is above all the portrait of a rose new to European art. Zurbaran''s still life was unusual in featuring one flower, artists of the seventeenth century generally favoured quantity as well as quality and, among the latest novelties to appear in flower paintings, roses earned a central position.

Mignon included the many-petalled centifolia rose (the pride of rose breeders), the even newer bicoloured rose and a single yellow rose, while van Huysum''s rarest flower was a double yellow rose. Some symbolism remained, among these exquisite petals insects rummaged as a reminder of mortality (the same preoccupation that the contemporary artist Mark Quinn seeks to express with his silicon flowers frozen in a false, perpetual bloom). The diversity of rose symbolism grows with every century and becomes more enigmatic - Manet''s rose in a brioche, Klee''s rose garden and Dali''s surreal red rose suspended in a blue sky. The idea of painting flowers against the sky first arrived in Europe from Japan with woodcut prints, just in time to inspire the Impressionists in the use of different viewpoints and bold blocks of colour. Otherwise Renoir might never have stared diagonally downwards on a bed of dahlias, nor Caillebotte crouched among his chrysanthemums, nor Monet gazed across the watery expanses of his lily ponds allowing the sky to appear only in reflection. But the sky itself was Van Gogh''s, whether he was painting starry constellations, dark crows or branches of spring blossom. He was so fascinated by Japanese art that he copied Hiroshige''s print of the Plum Blossom of Kameido (and his Bridge in the Rain) and tried to absorb the philosophy behind them. Above all there was the question of reality, a challenge for every generation of artists - because inevitably they deal in illusions.

In the West the bias of flower painting had (until the Impressionist movement) been towards achieving scientific accuracy, while in the East the artist''s skill lay in capturing the sense that the plant was alive - as Dylan Thomas put it: ''the force that through the green fuse drives the flower''. This was not necessarily done by observation, rather by a lifetime of seeking harmony with nature, refining the necessary techniques and the discipline of endless repetition, in order to achieve perfect self-expression. This may help to explain how flower painters as diverse as Van Gogh, Charles Rennie Mackintosh and Elizabeth Blackadder all emulated the energy and refinement of Japanese aesthetics. While for Monet the idea of creating a series of the same subject in varying conditions, which led finally to his lily ponds, owed much to Japanese prints grouped under titles such as One Hundred Views. The wisteria which he painted as his eyesight failed, in abstract calligraphic patterns but still unmistakeably wisteria, was Japanese both in origin and style. Above all, Japanese prints helped to release colour from the confines of straightforward imitation. This was the context in which Gauguin as well as Matisse, and even Picasso, were influenced by Japanese prints, and became extravagant with colour in a manner loosely termed Symbolist. When a seventeenth-century artist like Jan Breughel painted a cyclamen, it was a tiny delicate thing among a great arrangement, or else placed on a ledge beside a central vase as a wondrous little botanical specimen complete with its rooty corm.

When Matisse painted a cyclamen it was a triumph of pink against blue, large startling and vibrant. Although Matisse''s version was less realistic he demanded more strongly that one consider the flower itself. Similarly when Bosschaert painted a tulip, the streaks of colour that made it fabulously expensive were exquisitely and precisely defined, but when Duncan Grant painted tulips their vitality sang out from the canvas in a blur of colour. Matisse and his followers opened the way for a purely abstract artist like Patrick Heron who described entering a greenhouse and seeing ''a violet flower with five petals suspended against the receptive furry green leaves'' as ''the terrific zing of a violet vibration''. One suspects the flower was an African violet, the words describing it are superb, but alas with abstraction the individual flowers are quite lost. This was the risk inherent in Kandinsky''s belief that ''colour and form should no longer be indebted to outward appearances in nature but to the feelings and inner world of the artist''. But modern art contains many traditions and often makes reference to the art of the past. When Howard Hodgkin painted a lotus flower with a brush full of green paint, simply forming a V shape against green rectangles, he described the place in India where they grew as a ''Douanier Rousseau garden'', which helped to add a humid jungle atmosphere to the flowers he sought to evoke.

When the Surrealist painter Dorothea Tanning used a sunflower as a threatening image was she expecting everyone to think of Van Gogh''s sunflowers? Which brings the questions surrounding artists'' flowers back to roses, and whether Dali meant his surreal red rose to be a celestial or a sexual symbol. Flowers continue to exercise a powerful spell and to be full of hidden meaning, but for those who prefer them less abstract and less complicated, Stanley Spencer was heroic in his simplicity. He placed flowers back among the earth and walls of cottage gardens, happy and sensitive in the warm light. His loving description of snowdrops waiting to be painted could apply to any flower: ''They were fearfully pleased with themselves. You could imagine them discussing it. "he''s come right to where we are with a camp stool, there''s something up.I knew there was something about us".''.