A reader in Allentown, Pa., wrote to ask questions about "air fern." Is it really a live plant? Does it come from the ocean; If so, why doesn't it have to be in water? If it is a plant, how tall does it get, how long will it live, and why doesn't it need water or fertilizer?

The "air fern" is not a plant. The filmy green plume sold as air fern or neptune plant is the dried and dyed skeleton of a filamentous aquatic animal identifed by zologists as an ocean-dwelling "moss animal," Bugula. It is found growing under water on rocks or floating pieces of wood off the English or Norman coast. It is not a fern: It is not a plant. It will not grow.

A reader who is a collector of rare plants asks where she can find a papyrus plant.

The Egyptian paper plant, Cyperus papyrus, is listed in the catalog of Three Springs Fisheries, Lilypons, Md. (near Frederick). It is a good water plant in pools outdoors but must be taken indoors for winter protection. A wide variety of pool plants as well as pool equipment is available from Three Springs, which is located at a convenient driving distance from Washington. The famous operatic soprano, Lily Pons, gave permission for use of her name as the mailing address.

A reader asks when can she plant the spadix of her Peperomia.

Peperomias are usually propagated by leaf or stem cuttings. Unless she is sure that there are fertile seeds, which she can remove from the spadix (flower stalk) for planting, she will have better luck propagating her plant from cuttings. Seed of one species, Peperomia maculosa, is listed in the catalog of Geo. W. Park Seed Co., Greenwood, S.C. 29647.

Mrs. John Edwards of Springfield, Va., writes: What are the chances of successfully air-layering a young, tall, skinny Ming Aralis? Also, what can be done about minute flying insects that live in baskets of ferms lined with spagnum moss.

According to James Underwood Crocket, author of Foliage House Plants (Time-Life Encyclopedia, 1972, $7.95), the propagation of Aralias is neither easy nor impossible. Crockett suggest growing Aralias from stem cuttings set in coarse damp sand. Cover the cutting with a plastic bag or glass jar, place it out of the sun and mist frequently. When the cutting is routed, pot it in any good growing mix.

If you are experienced with air layering there is no reason not to try it, but cuttings are easier. I have found no authoritative reference on use of air layering for Aralia.

The small black flying insects are fungus gnats, frequently a sign of overwatering. Allowing the soil surface to dry out between waterings is probably the best control. Where drying out is not feasible, plants can be watered with a solution of one teaspoon chlorine bleach in one quart of water. Another way of coping with these pests is Black Leaf 40 at the rate of one teaspoon to two quarts of watet with a little soap added. Pour a little of this solution on the soil surface.

If you or your plants are not averse to chemical pesticides, a soil drench of Diazinon may be used. When using pesticides, always be careful to follow directions given on the container. Pesticides arepoisonous.