Q: What are the differences between short- and long-grain rice?

A: These names refer to grades used by rice millers and growers. Short grains are usually fatter and take longer to cook. The longer cooking time means the outer layer of each kernel absorbs more water, its starch granules burst and the grains begin to stick together. For that reason, short-grain rice is used in risottos (rice baked or boiled to a creamy consistency in an open pot with stock) or molded rice side dishes or puddings.

Long-grain rice is thinner and therefore requires shorter cooking time. It produces the fluffiest, least sticky cooked rice.

Q: What is celery knob? To what degree is it related to the celery stalks one serves as appetizer or flavoring in soups and stews? How does one prepare this ugly but apparently tasty root? I tried washing and peeling it with a potato peeler, cut it in cubes and boiled them in lightly salted water. Each piece had a sliver of woody peel attached to it.

A: Celery knob is also called celeriac, turnip-rooted celery, celery root or celery rave (pronounced "raahve"). It has pine-green "stems" (actually petioles or leaf-stems) resembling those of its wild ancestors that still populate marshes of western Europe. The knob -- an enlarged root which also serves as stem -- has a pronounced celery flavor, a cottony texture and an ivory color. On the outside is a quarter inch of lignified tissue (wood) that must be cut away with a paring knife.

The boundary between outer wood and inner soft tissues is easily seen. The external layers are whiter in color and less fibrous. They are similar to the outer layers of turnips and rutabagas. As with these vegetables, one peels celery root by cutting away the quite visible outer layer.

Celery is rich in the plant enzyme polyphenoloxidase, which is responsible for discoloration on exposure to oxygen. If you are paring a number of roots, rub them with lemon juice. The ascorbic acid (vitamin C) and citric acid will inhibit this discoloration reaction.

In Europe, celery root is a popular salad. It is shredded or cut into fine julienne (matchsticks). Because the root is just a little tough, they blanch the pieces (30 seconds in boiling, salted water) then mix them with mayonnaise and lemon juice. One might also prepare this salad with a vinegar-and-oil dressing.

Celery root salad has a remarkable freshness that blends into any leafy green salad. Its color and taste make it appropriate on a plate with other crudite's. It is the perfect platemate of carrot salad (dressed with lemon juice and olive oil), beet salad (dressed with garlic, vinegar and oil) and belgian endives (dressed with vinegar and oil).

Celery root also makes -- in combination with potatoes -- an excellent gratin. Peel and slice boiling potatoes as for scalloped potatoes. Bring these to a boil and simmer 5 minutes. Then add sliced celery root and cook until the potato slices are tender. Pour the liquid onto a blond roux (for every cup of liquid, heat 2 tablespoons melted butter and 2 tablespoons flour until a very light brown) and thicken as for any other cream sauce. Add a little cream or sour cream, season with salt and pepper and simmer 5 minutes. Arrange the potato and celery root slices alternately in a baking dish. Pour over them the cream sauce and top with shredded emmenthal (swiss cheese). Broil until golden (about 10 minutes) and serve.

Celery root is also a delicious stew and soup vegetable. Remember, however, that it has a strong flavor that can easily mask those vegetables and meats of more delicate character.