AMONG the many melons found in Asian vegetable markets, the angled luffa or ridged gourd invariably stands out. This is literally, as well as figuratively, true. Angled luffas are narrow, dark green melons, measuring only 21/2-5cm in diameter but up to 60cm in length; attractive and prominent ridges run the length of the melon, tip to base. Called see gwa in Cantonese, they are grown and eaten throughout Southeast Asia and southern India. More famous, perhaps, than the angled luffa is its cousin, the sponge luffa (or ''loofah'' or soi gwa in Cantonese). This melon also appears in markets in its younger years. It has the same dark green, rather rough textured skin of the angled luffa, butlacks the ridges - with its skin marked by longitudinal lines instead - and looks much more like a fat cucumber. Generally, the Cantonese stir fry angled luffa with chunks of onion, wood ear mushrooms, ginger, and slices of fresh fish. The sponge luffa is recommended for soup, best boiled for an hour or two with port bones or meat. Elsewhere in Southeast Asia and southern India, both luffas are served in curries as well as in soups. In the Western kitchen, angled luffa can be steamed, boiled or sauteed in the same way as courgettes or summer squash. Sponge luffas are typically short and stout, 5-71/2cm in diameter, and seldom more than 20cm in length. Only young ones - as found in the markets - are eaten; older ones are left on the vine to ripen. As they mature, the flesh becomes tough and fibrous.This mesh of fibres - dried, skinned, and bleached - is the familiar sponge ''loofah'' sold for cleaning and bathing. Here, as elsewhere, the angled luffa is far more popular and widely consumed as a vegetable. Sponge luffas reaching markets are primarily thinnings culled from vines which already bear enough fruits for sponges. Buying and storage. In both cases, select younger melons, as the older ones develop a somewhat unpleasant, bitter flavour. For the angled luffas, quality correlates with resilience or ''bounce''. The trick to testing this characteristic is to pick one upby the stem end and waft it very gently in the air. If young, it will bounce slightly. If old, it will be as stiff as a broom handle. And if you are too vigorous, it will simply break off in your hand, so waft with care. Both luffas can be stored, refrigerated, for at least a week. Preparation. For the angled luffa, first remove the ridges with a vegetable peeler or small knife. If the melon is young, leave the skin between the ridges intact. This creates attractive longitudinal stripes and will provide a pleasant contrast in flavour and texture in the finished dish. The Cantonese often cut the melon into wedge-shaped pieces rather than into simple rounds. To do this, lay the melon on the chopping board, hold the knife diagonally above the melon, whack off a small piece, then roll the melon approximately one-quarterturn, and whack again (without changing the angle of the knife). Cooking. No matter what the method, remember that the melon's soft, spongy central flesh tends to collapse as it cooks. To serve it as a side vegetable, cook it quickly over fairly high heat to preserve colour and texture. Martha Dahlen, a botanist and food writer, has lived in Hongkong for 15 years. She is the author of A Cook's Guide to Chinese Vegetables, (Guidebook Co, $110).