Flowers so splendid and common

''My limited and abstracted art,'' wrote the English landscape painter John Constable in 1832, ''is to be found under every hedge, and in every lane, and therefore nobody thinks it worth picking up, but I have my admirers. . . .''

Like the Northamptonshire poet John Clare, Constable was greatly in love with the landscape of his childhood (in his case a particular part of Suffolk), and not only with its large facts of sky, weather and cultivation, but also with its unobtrusive and overlooked details. ''The fields grow old and common things,'' Clare wrote, and Constable painted the same idea. This is certainly true of his study of poppies: there could hardly have been a commoner flower of the field. One plant can produce 17,000 seeds; a meadow, like a sea of redness, can contain hundreds of millions of potential plants. And Constable, rather like a delighted child suddenly seeing a poppy for the first time, isolates a plant, his ''limited and abstracted art'' - separating it decisively from the crowd as a subject of rare beauty. What Margaret Drabble has said about Clare might as easily apply to Constable's affection for such a familiar weed: ''. . . the word 'common,' by an extraordinary shift of meaning, which shifts the meaning of man's relation to the whole world, comes to signify, in Clare's language, the wonderful, the rare, the vanishing, the highly prized.''

Constable has intensified his poppy's value by adapting to his own purposes the 17th-century practice of highlighting flowers against a dark background. The deep brown of the ground on which the study is painted vivifies, by contrast, the sunlit red of the flowers, and vitalizes the sharp green of the leaves, bud and stems. It even makes it possible for him to depict clearly the minuscule bristles or hairs on these wiry stems, and to follow their slightly twisting awkwardness. A wonderful touch is that Constable painted the very top of the stems red, rather than green, observing how the sun, filtered through the semitransparent petals, projects their hue.

There are more surviving drawings of plants and flowers by Constable than there are painted studies. I suspect that his special tribute to the poppy, so inextricably associated with summer fields, was partly connected with a colouristic trick or trait he had developed in his paintings over the years. It had almost become a trademark. His pictures of fields, trees and lawns in summer amount to a virtual celebration of the colour green. No one has painted the greenness of grass - lush with new, rain-bright growing - as Constable has. This looks natural enough to our eyes, but at the time it was unconventional: browns and ochres, autumnal colours, were considered more suitable for landscape paintings. But, as C. R. Leslie, his friend and biographer, put it, Constable's trees and grass ''are of the freshest green'' because he ''could never consent to parch up the verdure of nature to obtain warmth.'' However, this naturalism on Constable's part did mean that his paintings of even the sunniest and warmest time of year were predominantly in a ''cool'' colour. His ''trademark'' was the introduction, in small patches, of the colour red, in whatever guise seemed fitting: a farm worker's jacket, a small boy's waistcoat, a horse's harness, a bargeman's hat - or poppies in the corn. Such spots and accents of red in the landscape, though small, act strikingly as a sufficient and enlivening counterbalance, not only to green, but to the cool, clear blue and white of his typically exhilarating skies, and to his use of white specks and dashes of pigment to give the entire picture dewy sparkle and breeziness. He must also have known (well in advance of the Impressionists and Van Gogh) that the opposition of red and green made both seem more alive. This oil study of poppies seems to me to be Constable's grateful recognition that it was nature itself that splendidly provided him with one of the delights of his art: brilliant spots of pure, fresh red - poppy red - to complement its ubiquitous viridity.